Untapped Potential? A Survey Study with German Police Officers into Suspect Interviewing Practices and the Strategic Use of Evidence

ABSTRACT The Strategic Use of Evidence (SUE) technique is a promising suspect interviewing approach that takes the potentially incriminating information against a suspect (i.e., the evidence) into account and aims at actively eliciting diagnostic cues to deception and truth. The technique was successfully tested in multiple research studies and has been introduced to practitioners in different parts of the world (including Germany). However, not much is known about German police officers’ state of practice, their knowledge, as well as how they perceive and evaluate SUE. The current survey study is the first attempt to generate knowledge on this topic by collecting data from police officers from the states of Schleswig-Holstein and Hamburg. The majority of police officers kept a balance between applying non-standardized/standardized interviewing approaches, discussing preplanned/spontaneous themes in the interview and making analytical/gut decisions on when and how to use evidence during suspect interviews. Regarding their suspect interviewing training, only a minority of the officers reported to have received training on how to use evidence during an interview. These findings – in combination with the observation that the majority of the officers did not see potential obstacles with the applicability of the SUE technique – suggest a major untapped potential of strategic evidence disclosure techniques within current suspect interviewing in Germany.


Introduction
Investigative interviewing is a major purview of police work. Based on the interview, police make judgments on the veracity of the person questioned. However, research has repeatedly shown that people with no special aids or training perform at chance level when asked to discriminate truths from lies (Bond & DePaulo, 2006;Kraut, 1980;Vrij, 2008). In contrast to what one might expect, presumed lie experts (e.g., law enforcement officers and legal professionals) often do not achieve accuracy rates that exceed those of lay people (Bond & DePaulo, 2006). The poor performance can be explained by the scarcity and low validity of objective cues to deception resulting in a low predictive value of behaviors that have at least some relation to deception (e.g., DePaulo et al., 2003;Hartwig & Bond, 2011). To help people make more correct veracity judgments, it is important to increase the behavioral differences between liars and truth tellers. A possible course of action is to develop techniques that either elicit new diagnostic cues to deception or increase the predictive power of the few already existing cues (e.g., Hartwig & Bond, 2011).
An interviewing technique that can help improve people's ability to make correct veracity judgments is the Strategic Use of Evidence (SUE) technique (e.g., Hartwig, Granhag, Strömwall, & Kronkvist, 2006;Hartwig, Granhag, Strömwall, & Vrij, 2005). SUE is a strategic interviewing technique that takes the potentially incriminating information against a suspect (i.e., the evidence) into account and aims at actively eliciting diagnostic cues to deception and truth. The development of the technique started in the early 2000's in Sweden (Hartwig, 2005). During the last one and a half decade, the technique has been introduced to a small number of practitioners in different parts of the world through lectures, training courses (given mainly by the developers) as well as scientific publications (e.g., . In Germany too, some legal psychologists and legal practitioners are familiar with the SUE technique and provide basic training at some German Police Schools to police officers-in-training and advanced training courses to practitioners in the field (L. May, personal communication, June 4, 2019). However, nothing is known about how the SUE technique is perceived and evaluated by German police officers.
In the current study, we chose to focus on the SUE technique for multiple reasons. First, SUE is a promising, innovative and scientifically solid interview approach thatunlike most other interview approacheshas a strong theoretical foundation (e.g., Clemens, 2013). Second, SUE is an interview approach that takes the available evidence against a suspect into account. Considering that the interviewer often has some sort of evidence against the suspect (e.g., Wagenaar, van Koppen, & Crombag, 1993), it is essential to find effective ways to disclose it. Third, extensive empirical research over the last one and a half decades has shown that the SUE technique is effective at eliciting diagnostic cues to deception (for a meta-analysis see Hartwig, Granhag, & Luke, 2014; see also Brimbal & Luke, 2019). Consequently, the SUE technique, which represents a considerable alternative to common (more or less) ineffective and questionable interview techniques, deserves further empirical attention.

The strategic use of evidence technique
Theoretical framework The framework from which the SUE technique is derived is based on psychological research on suspects' strategies and their verbal behavior in interviews . Research shows that innocent suspects, regardless of whether they are informed about the evidence against them or not, typically disclose all the information they recall because they feel they do not have anything to hide. In contrast, guilty suspects disclose information dependent on how much and what evidence they believe the police hold against them. In other words, their perception of the evidence informs their decision of what to deny, withhold, or divulge (Moston & Engelberg, 2011;Tekin et al., 2015). If guilty suspects know, or at least believe, that the interviewer holds incriminating evidence (e.g., because it was disclosed at the beginning of the interview), they would commonly provide a story that explains the existence of the evidence with a noncriminal motive . However, if guilty suspects do not know or are unsure about the potentially incriminating information against them, they have the tendency to either avoid mentioning or to deny holding this information in order to avoid selfincrimination and to appear innocent (e.g., Granhag, Clemens, & Strömwall, 2009;Hartwig et al., 2005). The verbal behavior resulting from avoidance and denial leads to inconsistencies with the evidence. Such statement-evidence inconsistencies can be used as a diagnostic cue to deceit (Hartwig et al., 2014). Several studies have shown that using the evidence in this strategic manner results in significantly more statement-evidence inconsistencies in guilty suspects' statement than innocent suspects' statements (for a meta-analysis see Hartwig et al., 2014; see also Brimbal & Luke, 2019).

The SUE components
The assessment of the case-related evidence prior to the interview is the first phase of the SUE interview (Evidence component) (Granhag, 2010). In light of the theoretical framework, the interviewer needs to assess the evidence along two dimensions. First, the interviewer needs to determine the diagnostic value of a possible statement-evidence inconsistency. The value is higher if it can be attributed to the suspect's strategy to withhold/deny information (in an attempt to conceal criminal activities) rather than other factors such as memory errors 1 . Second, the interviewer needs to evaluate the probability that the suspect knows if the interviewer holds a certain piece of evidence 2 . A piece of evidence is specifically valuable when the diagnostic value of its potential inconsistency with a suspect's statement is high and the probability of the suspect knowing that the interviewer holds this certain piece of evidence is low 1 For example, the activities of the suspect suggested by a picture taken at the crime scene the day before an interview should still be readily available in the suspect's memory. In that case, failure to mention or denying that s/he had been to the crime scene is of higher diagnostic value than had the picture been taken three months ago.
2 For instance, if the photo in question was taken at a monitored public place or store, it is likely that the guilty suspect knows that the interviewer is in possession of this evidence. Consequently, the guilty suspect will probably present a story consistent with what the photo suggests resulting in no statement-evidence inconsistencies. In contrast, if the photo was taken at an unexpected place (e.g., in the wild), the suspect probably will not expect the police to be in possession of such information. Consequently, s/he will deny his/her presence at the crime scene leading to a statement-evidence inconsistency. (Granhag, 2010). Following the assessment of the evidence and the decision on how to utilize each piece (i.e., if, when and how to disclose the evidence to the suspect), the interviewer starts the interview by giving the suspect a chance to provide his/her side of the story through open questions (Question component) (e.g., . The interviewer then asks a series of specific questions about the evidence without revealing the true purpose of the question (e.g., questions about the suspect's activities on a certain day rather than asking about his/her visit to a certain store that day, of which a surveillance video exists). The specific questions aim to systematically exhaust alternative explanations of the available evidence. Once the suspect's story is obtained and the alternative explanations are exhausted, the interviewer reveals the evidence and asks the suspect to clarify any statement-evidence inconsistencies that occurred in response to the previous questions (Disclosure component). For this phase, the interviewer makes tactical decisions with regard to the timing of the disclosure. For instance, each piece of evidence can be revealed at the end of the interview (e.g., Hartwig et al., 2005) or in a stepwise manner throughout the interview (e.g., Tekin et al., 2015). The interviewer may also frame the evidence based on the strength of its source and its specificity 3 (for a more detailed account, see Granhag, Strömwall, Willén, & Hartwig, 2013;Vrij & Granhag, 2012).

Criteria for practical use of SUE
For the SUE technique to be applicable, various prerequisites have to be met. First, the suspects must be willing to make a statement. If suspects use their right to remain silent (as described in § 136 para. 1 of the German Code of Criminal Procedure) or do not show up for the police interview, the SUE technique cannot be used. However, research has shown, that most suspects do not make use of their right to remain silent (e.g., Moston, Stephenson, & Williamson, 1993;see Volbert, May, Hausam, & Lau, 2019 for a German sample). Second, potentially incriminating crime-relevant information, that can be used in a strategic manner, needs to be available. As the interviewers often get their hands on some sort of evidence against the suspect in the course of the investigation, this concern is in general unwarranted (e.g., Wagenaar et al., 1993). Third, it is important that suspects are unaware of the evidence against them before the first interview. Otherwise, suspects can easily adapt their statements to the evidence they know the police hold. In Germany, the defense lawyer and the defendant may be denied access to the case file which lists the evidence if such access endangers the police investigation ( § 147 para. 2 of the Code of Criminal Procedure).

3
The source of the evidence can be framed as weak ("We have information telling us that … ") or as strong ("We have surveillance camera footage showing us that … "). In addition, the specificity of the evidence can also be framed as low (" … you were visiting a store") or as high (" … you were buying item xy").
In summary, there seems to be no objective structural hurdles in the German legal context for the SUE technique to be applied. However, it is yet unknown whether police officers in Germany perceive the technique as applicable based on their everyday practical experiences and whether they see value in changing from their current interviewing practices to a more systematic approach of suspect interviewing as put forward by the SUE technique.

Police interview techniques in Germany
Although German police officers are largely free in the choice of interview methods they want to use, suspect interviews must adhere to state and federal law. At a federal level, the criminal procedural law prohibits inhumane methods, such as the use of consciousness altering substances, hypnosis, psychological and physical pain and the presentation of false evidence ( § 136a para. 1 of the Code of Criminal Procedure). At state level, each stateor Bundeslandhas its own police force and autonomously establishes training content and guidelines regarding investigative interviewing. In addition, the organization and the duties of the police are subject to the law of each state (Frevel, 2008).
The Federal University of Applied Administrative Sciences provides various examples of possible interview methods (Conring, 2008(Conring, , 2016. This information is based on multiple publications of practitioners and forensic researchers in Germany (e.g., Artkämper & Schilling, 2014;Feldmann & Hennings, 2010). Thus, German police officers (including Schleswig-Holstein and Hamburg) could be taught or informed about the following interview methods: (a) Exploratory method ("Sondierungsmethode"). This is the most commonly used method in Germany (e.g., Conring, 2008;Steinert, 2012). After careful preparation, the interviewer begins the interview by building rapport with the suspect to reduce inhibitions and/or tensions as well as trying to gather information about the suspect (e.g., his/her intellectual or language capabilities, opinions and motives) (Rapport Phase). Then the interviewer starts the actual interview first by sharing information on the suspect's charge and his/her procedural rights (Information Phase). The interview is divided into two consecutive phases: the narrative phase and the questioning phase. In the narrative phase, the interviewer gives the suspect the opportunity to tell everything relevant to the incident in question. This is followed by structural questioning; that is, questions start off as general and gradually become more specific (funnel technique). Subsequently, the suspect is confronted with any contradictions that occur in response to these questions. (b) Determination method ("Festlegungsmethode"). The determination method can be used if the suspect is believed to be lying. In this interview method, the available evidence is withheld from the suspect during the questioning phase. Once the suspect's statement is gathered, the interviewer confronts the suspect with the inconsistencies between his/her statement and the available evidence. This method aims to create an overwhelming and surprising situation with the purpose of obtaining a truthful statement. This method appears to be rather similar to the Question and Disclosure components of the SUE technique. (c) Persuasion method ("Überzeugungsmethode"). This method is used only if the suspect refuses to provide a statement before or during an interview. The aim is to convince the suspect to provide a statement through the use of rational and emotional arguments. (d) Surprise method ("Überraschungsmethode"). In this interview method, the interviewer confronts the suspect right at the outset of the interview with the allegations and the evidence. The surprise aims to obtain a confession from the suspect. This interview method is legally controversial, as the police provoke a reaction/statement from the suspect without having informed him/her on the accusation, his/her right to silence and his/her right to have an attorney. (e) Rapid-fire questioning ("Zick-Zack Methode"). This method is characterized by rapid questioning and constantly changing the topics of the conversation, which exerts a high cognitive demand on the suspect. This procedure aims to make it more difficult for the suspect to maintain his/her lies. There are legal concerns about this practice, as deliberate confusion and cognitive pressure can lead to false confessions (e.g., Kassin, 2008). (f) Reid technique ("Reid-Methode"). The Reid technique (Inbau, Reid, Buckley, & Jayne, 2013) is one of the most widely used suspect interrogation procedures by police officers in the United States of America.
Following an initial evaluation of the suspects' veracity based on their behavior (Behavior Analysis Interview), suspects who are believed to be guilty are interrogated with the aim of eliciting a confession (9-step interrogation). To fulfill this aim, Inbau et al. (2013) recommend the use of psychological manipulation varying from isolating suspects from their families to presenting false evidence. Especially two types of approaches are prominent in the 9-step interrogation. The first typeminimizationis "a technique in which the detective lulls the suspect into a false sense of security by providing face-saving excuses, citing mitigating circumstances, blaming the victim, and underplaying the charges" (Kassin & Kiechel, 1996, p. 125). The second typemaximizationis an approach "in which the interrogator uses scare tactics by exaggerating or falsifying the characterization of evidence, the seriousness of the offense, and the magnitude of the charges" (Kassin & Kiechel, 1996, p. 125). In the early 2000's a few Reid courses were offered in Southern Germany but were discontinued in the years after (Kroll & Feltes, 2016). Today, the manipulative Reid technique is prohibited in Germany because it is in violation of § 136a para. 1 of the Code of Criminal Procedure (e.g., Conring, 2016).
In addition to learning about these methods, the training of the police in Schleswig-Holstein and Hamburg involves going through practical exercises in legal psychology (e.g., deception detection, credibility, suggestibility, eyewitness memory, eyewitness identification). Further, there are optional courses offered to police officers, such as seminars in Schleswig-Holstein on criminal police interviews and criminal police interviews in serious crimes (K. Kahlo, personal communication, April 2018). However, it remains unclear how thoroughly the individual topics are covered and to what extent the contents are based on current psychological research.
In summary, German police officers receive training in various interview methods. However, neither at federal level nor at state level does an official "interviewing manual" exist that lists the interviewing techniques that must be taught mandatorily. The most widely used exploratory method corresponds with the information-gathering approach, whereas most of the other common methods correspond with a confrontational approach. However, purely accusatory and manipulative approaches are legally prohibited (as described in § 136a para. 1 of the Code of Criminal Procedure). Beyond that, although it is possible that some instructors (police, criminal specialists, and psychologists) cover aspects of the SUE technique in their classes, neither the state police in Schleswig-Holstein and Hamburg nor the German federal police receive official training in the SUE technique.

Research aims
Researchers emphasize the importance of exchanging knowledge between scientists in the field of suspect interviewing and practitioners (Vrij & Granhag, 2012). In line with this view, we argue that researchers should explore practitioners' attitudes toward new innovative interview methods (like the SUE technique) as well as the value and obstacles they may see in using these methods in their daily work. For example, a recent study conducted with police officers in the UK showed that the respondents reported using statement-evidence inconsistency more than any other inconsistency type to detect deception, and that they believed it was the easiest type to assess (Deeb et al., 2018). This finding clearly demonstrates a compatibility of existing working routines of English and Welsh police officers and the use of the SUE technique. According to Granhag and Hartwig (2015), the guidelines provided by the SUE technique can easily be combined with "already established and ethically sound frameworks for investigative interviewing, such as the PEACE-model (used in the United Kingdom), The General Interviewing Strategy (used in the Netherlands), and the KREATIV-model (used in Norway)" (p. 246). Beyond that, we are aware of some research efforts that have been made to explore whether and how police officers in the UK, the Netherlands and Norway use evidence strategically in their interviews (e.g., Tekin, Granhag, Strömwall, & Vrij, 2016;Walsh, Milne, & Bull, 2016). However, little is known to date about how German police officers interview suspects and how they would evaluate the strategic use of evidence. To address this gap in the literature, the aim of the current study is threefold. First, we want to examine police officers' state of knowledge and practice when conducting suspect interviews to get an understanding of whether there is a demand for police officers to learn about the SUE technique as a strategic interviewing approach. Second, we want to examine whether the police officers are familiar with the different components of the SUE technique andif sowhich SUE components they already use in their working routines. Third, we want to determine how the police officers assess the applicability of the SUE technique (e.g., whether they anticipate problems in the German context). As a first attempt to close this gap of knowledge, the current study used a sample of German police officers from two German states (Schleswig-Holstein and Hamburg).

Data collection and participants
In Schleswig-Holstein, 300 paper-and-pencil questionnaires were sent to the 30 departments of relevant crime areas. These departments handle crimes like murder, severe robbery, sex crimes, and arson. In Hamburg, the questionnaire was sent out via e-mail to 134 police officers from departments that handle crimes like capital offenses, sex crimes, and arson. These departments were selected because (a) police officers typically deal with a variety of evidence, and (b) the time interval between the crime and the first interview is typically short, which restrains the suspect from preparing by inspecting the investigation file beforehand (J. Vullgraf, personal communication, October 7, 2016). These two features are important prerequisites for the SUE technique to work. The respondents were given two weeks to fill out the questionnaires. The response rate was 40.7% (n = 122) in Schleswig-Holstein and 60.0% (n = 75) in Hamburg 4 . Of the 197 participating police officers, 128 were male (65%) and 69 were female (35%). No significant association was found between gender and state (Schleswig-Holstein vs. Hamburg), χ 2 (1) = 1.32, p = .25. The age of the respondents ranged from 22 to 60 years (M = 41.54; SD = 11.47) and the professional experience ranged from 1 to 41 years (M = 15.46; SD = 10.72). The respondents in Schleswig-Holstein were significantly older (Schleswig-Holstein: Mdn = 47; Hamburg: Mdn = 37, U = 3499, z = − 2.77, p < .01, r = − 0.20) and more experienced (Schleswig-Holstein: Mdn = 18; Hamburg: Mdn = 12, U = 3757.0, z = − 1.97, p = .049, r = − 0.14) than the respondents in Hamburg. The majority (n = 114, 93.4%) of the police officers from the Schleswig-Holstein sample were trained in Schleswig-Holstein, the majority (n = 71; 94.7%) of the police officers from the Hamburg sample were trained in Hamburg 5 .

Procedure and material
Respondents were first informed about the purpose of the study and that their participation was voluntary and confidential. Respondents were asked to fill in the questionnaire, which consisted of six demographical questions and 16 questions (including follow-up questions) about their training, work practice, knowledge and assessment of the SUE technique. In the following, we will only report the questions that are relevant to the current study's aims (see Appendix A for the list of analyzed questions). The first section of the questionnaire addressed more specific aspects of the officers' training on suspect interviewing (items 1, 1a, 2, 3 and 4). Specifically, we asked police officers about the interviewing techniques they were instructed in during their (basic and advanced) training (training on suspect interviewing, training on evidence use). Thereafter, they answered questions regarding their work routine when interviewing suspects (items 5, 6 and 7) (standardization of procedure, preplanned theme selection, and analytical decision-making on evidence use/disclosure) and self-assessed their level of knowledge in suspect interviewing and their deception detection abilities (items 8 and 9).
The second section consisted of a brief summary of the SUE technique (including the three components of the tactical level) after which the officers answered questions with regard to their familiarity with the three SUE components (item 10) (i.e., how well they knew the components) and the extent to which they use these components in practice (item 11).
Lastly, to generate information on officers' assessment of the applicability of the SUE technique, we first asked officers to recall from their memory how often the prerequisite of the SUEthe suspect not knowing about the evidenceis met in suspect interviews (item 12). Second, we asked the respondents to indicate whether they anticipated obstacles toward the applicability of the SUE technique in Germany andif they didto elaborate on the reasons for their belief (items 13, 13a). The questionnaire took approximately 15 minutes to complete.

5
As the comparison of the two states was not the focus of the current paper, we merged the data from the two groups and treated them as one sample.

State of knowledge and practice
Training on suspect interviewing In order to get an understanding of the state of knowledge police officers have on different interview methods, we asked them to report whether they received any input on suspects' interview methods during their (basic and advanced) training and which methods they were taught. The vast majority of police officers in the current study reported that they had received training about suspect interviewing techniques during their basic training (79.6% 6 , n = 156). In addition, roughly more than half of the police officers (57.1%; n = 112) participated in at least one advanced training course on suspect interviewing.
The exploratory method and the determination method were the most frequently taught interview methods both during basic and advanced training (see Table 1). Fewer officers reported that they had received training in the persuasion method, surprise method, and the rapid-fire questioning. Still, 10.2% of the police officers reported to have received training in (elements of) the Reid technique during their basic training, whereas 17.0% did during their advanced training. When asked whether they had received any other training except for the ones listed in the questionnaire, hardly any police officers indicated that they had (none of the officers indicated the SUE technique). Percentages reported in this paper are calculated based on the number of valid cases (i.e., officers who provided a valid response to the items in question) rather than the total number of officers who participated. Consequently, the N that the percent values refer to may differ from case to case.
Training on evidence use Given that the strategic use of evidence is an essential component of the SUE technique, we wanted to examine the extent to which police were already receiving training on evidence use. Only 20.9% (n = 40) of the police officers reported to have learned about how to use potentially incriminating information during a suspect interview. This finding demonstrates that there is a vast untapped potential to improving suspect interviewing by teaching police officers about the ways and benefits of (strategic) evidence use.

Standardization of procedure
The SUE technique provides a rather standardized framework and procedure that can be used as an orientation for practitioners when preparing and conducting their interviews but still leaves a sufficient degree of freedom for them to react in each individual situation. In order to assess the extent to which police officers adhere to a standardized procedure when interviewing suspects, they were asked to rate on a 5-point Likert scale (1 = always making a case-by-case decision, 5 = always using a standardized procedure). Table 2 shows that only one police officer of the entire sample (0.5%) reported to use a standardized procedure in all of his/her cases, whereas 22.4% reported that their applied procedure is always a case-by-case decision. The majority of the police officers (77.0%, n = 151) reported values between two and four on the scale indicating that their suspect interviews are characterized by both a certain degree of standardization and case-bycase decision making.

Preplanned theme selection
The Evidence component of the SUE technique assists interviewers to assess and organize the evidence before the interview begins. Such preparation can help to plan the themes one wants to address during an interview in advance. As a result, the interview procedure is more organized and easier for the interviewer to conduct. To determine the role of a preplanned theme selection in their work practice, we asked the respondents to rate the extent to which they prepared the themes they wanted to address in an interview on a 5-point Likert scale (1 = all addressed themes are spontaneous, 5 = all addressed themes are preplanned). The majority of police officers reported to strike a balance between a spontaneous and a preplanned theme selection for their suspect interviews (48.0%) or rather preplanned the addressed themes (39.3%) (values of 3 and 4 on the scale, see Table 2). However, none of the officers reported that the themes they addressed during a suspect interview were selected entirely spontaneously nor entirely preplanned (values of 1 and 5 on the scale) (M = 3.27, SD = 0.67).
Analytical decision-making on evidence use/disclosure The precise timing of the disclosure of evidence is a central component of the SUE technique. To withhold the evidence until all alternative explanations are systematically exhausted during the questioning phase requires an analytical assessment of the situation. To understand to what degree police officers already make analytical decisions in matters of evidence use (i.e., when to disclose it and how to use it), we asked them to indicate the extent to which their decisions are based on gut feeling or analytical thinking (5-point Likert scale; 1 = pure gut decision, 5 = pure analytical decision). Many officers (45.9%, n = 89) reported to keep a balance between gut-based and analytical decision making when deciding on when and how to use the evidence against a suspect during an interview (value of 3 on the scale). Only five of the police officers reported that their decision is purely analytical (2.6%) and seven reported that it is a pure gut decision (3.6%) (see Table 2).

Self-assessment
To establish how respondents assess their own interviewing skills, we asked them to rate their knowledge concerning suspect interviewing and their deception detection ability. Overall, the police officers assessed themselves quite positively on both aspects. That is, 92.9% of the officers (n = 182) perceived their knowledge on suspect interviewing as at least average or above (value of 3 and above on a 5-point Likert scale, 1 = very bad, 5 = very good). Similarly, most of the officers reported to believe that they are accurate in judging a suspect's veracity 70% (37.5%, n = 72) or 80% (22.4%, n = 43) of the time (see Figure 1).

Familiarity with/application of the SUE components
Of the three SUE components, the Evidence component was the least known among the police officers (5-point Likert scale, 1 = absolutely new to me, 5 = I already knew). Overall, the respondents reported moderate knowledge of all three SUE components (Evidence component: M = 2.57, SD = 1.25;

Assessment of the applicability of the SUE technique
In order to determine whether the SUE technique can be applied in real-life settings, the police officers were asked to estimate the prevalence of cases where the suspect has (almost) full knowledge of the evidence held against him/her. Almost all officers (80.7%; n = 155) reported that they never or rarely deal with cases in which the suspect knows about the evidence the police hold against him/her before the first interview (values of 1 and 2 on a 5-point Likert scale, 1 = never, 5 = always). Only five officers (2.6%) reported that they see these types of cases often (see Figure 2).
When asked directly whether they see potential problems in applying the SUE technique to their daily work, the majority of the police officers did not see any problems with the application of the SUE technique (71.1%, n = 140). Only a small portion (22.3%, n = 44) anticipated problems with the application of the technique 7 . To get a better understanding of the practitioners' reasoning, we additionally asked those who anticipated problems to elaborate on their assessment and analyzed their responses with a content analysis. First, two coders independently read all statements and created datadriven categories of anticipated problems. After discussion, the coders agreed on the final categories. Subsequently, the two coders applied the category system independently on 25% of the statements. Between one and three anticipated problems were listed for each officer. The inter-rater reliability was 81.3%, Cohen's κ = 0.78. Discrepancies were resolved in a discussion between the coders.
The identified categories of reported anticipated problems were expenditure of time (e.g., "Due to time pressure it is often not possible to deal intensely with these methods."), incompatibility with real-life complexity (e.g., "The concept is pretty rigid. The question is whether every actual [real-life] situation can be applied to it."), lack of suspect's willingness/capability (e.g., "Low intelligence of the suspect, suspect just answers with 'yes' and 'no', foreign suspects: interpreter"), doubts on the applicability of particular components (e.g., "The Evidence component sounds very abstract to me and I anticipate it to be difficult to implement in real-life settings."), interference with the natural suspect-interviewer interaction (e.g., "To adhere strictly to the technique could seem too rigid and artificial, so it could become more difficult to connect to the suspect."), and lack of (strong) evidence unknown to the suspect (e.g., "Often the evidence is not strong enough to convict him/her of lying."). Responses that were irrelevant to the question or could not be sorted into any of the existing categories and were too few (mentioned by less than five police officers) and too diverse to constitute distinct categories of their own, were coded as Other (e.g., "It is not known that the method was developed in Sweden. Instructions are unknown."). Table 3 provides the frequencies of the anticipated problems when applying the SUE technique.

Discussion
The Strategic Use of Evidence (SUE) technique is a strategic interview technique thatduring the last 15 yearshas shown its potential to actively elicit diagnostic cues to deception and truth in experimental research settings (e.g., Hartwig et al., 2014Hartwig et al., , 2005Jordan, Hartwig, Wallace, Dawson, & Xhihani, 2012;Sorochinski et al., 2013). Although the technique has been introduced to a smaller number of practitioners in different parts of the world (including Germany), no data exist on whether the SUE technique could add to the existing practices of German police officers and how they assess the applicability of the technique. By asking German police officers from two German states (Schleswig-Holstein and Hamburg) directly, this survey study aimed to fill this gap. Specifically, we examined the current police practice of suspect interviewing in Schleswig-Holstein and Hamburg, the respondents' familiarity with, and their use of, the three components of the SUE technique and their assessment of the applicability of the SUE technique.

State of knowledge and practice
In order to get an understanding of whether there is a demand for German police officers to learn about the SUE technique as a strategic interviewing approach, the first aim of the current study was to examine police officers' These mentioned problems could not be sorted into any of the existing categories and were too few (<5 cases) and too diverse to constitute distinct categories of their own. state of knowledge and practice when conducting suspect interviews. Specifically, we looked at three different components of officers' interviewing routines (i.e., standardization of procedure, preplanned theme selection and analytical decision-making on evidence use/disclosure).
To begin with, the majority of the police officers in our study reported a combination of standardization and case-by-case decision making when interviewing a suspect. Empirical evidence has shown the superiority of standardized interviews compared to non-standardized ones. For example, the Cognitive Interview (CI) which is a standardized interviewing technique and has been tested in approximately 100 laboratory experiments typically elicits 25% to 50% more information and generates comparable or slightly higher accuracy rates than the comparison interview (see Köhnken, Milne, Memon, & Bull, 1999;Memon, Meissner, & Fraser, 2010, for meta-analyses;Fisher, Ross, & Cahill, 2010, for a review of the research). The finding that roughly one out of four officers always makes decisions on a case-by-case basis can be seen as a sign that more standardized interviewing techniqueslike the SUE techniqueare needed to help practitioners prepare and conduct interviews in a systematic manner. Having said that, we cannot eliminate the possibility that the term "standardized" might have been interpreted by the respondents in a different way than we intended. While the term was meant to refer to an interview approach that can help practitioners to prepare and conduct suspect interviews with the aid of a framework providing general orientation for practitioners during the interview process, it might have been misunderstood as an overly rigid approach. For example, we cannot eliminate the possibility that the officers in our sample might have read that kind of standardization as unnecessarily inflexible and uncharacteristic of the way they actually question suspects. However, nothing could be further from the truth given that the SUE technique allows practitioners to easily adapt their course of action depending on the individual situation and/or person they are dealing with. As we did not further investigate respondents' answers, these concerns are merely theoretical and should be addressed in future research.
There is further reason to believe that incorporating the SUE technique into police practice in Germany might add value. As described above, standardized frameworks like the SUE technique, which is characterized by decisions before the interview on which themes to select and which evidence to disclose, outperform non-standardized interview approaches. While the police officers in our sample indicated that they keep a balance between (a) preplanning and spontaneously deciding on the themes that they wanted to address during the interview as well as (b) making decisions analytically and gut-based with respect to when and how to use evidence during suspect interviewing, providing training on how to use these frameworks should lead to more effective decision-making. In fact, only 20.9% of the respondents reported having received training on the use of potentially incriminating information. This finding is noteworthy considering that evidence, which could be strategically used in a suspect interview, is usually available after a crime (e.g., Wagenaar et al., 1993). In addition, research has shown that a considerate (strategic) use of the evidence will lead to more diagnostic cues to deception than an inconsiderate (non-strategic) approach (for a meta-analysis see Hartwig et al., 2014). In sum, these findings suggest that the potential for strategic evidence disclosure techniques during suspect interviews in Germany is still untapped.
The findings on the suspect interview methods the respondents were trained in are mixed and require further examination. On the one hand, the majority of the police officers in our sample had received training in the exploratory method and the determination method. As these methods bear a resemblance to the SUE technique, this finding shows that there is a sound foundation for the successful adaptation of the SUE technique in Germany. On the other hand, there was also a number of police officers who reported that they have received training in (elements of) the Reid technique which is associated with the risk of false confessions (e.g., Gudjonsson, 2003;Kassin, 2008;Kassin & McNall, 1991) and is prohibited in Germany. A possible explanation for this finding could be that in the early 2000's a few Reid courses were held in Southern Germany (Kroll & Feltes, 2016). Consequently, fragments of these training contents might have survived in the Police education system. As there is no research to date that could speak to the exact interviewing practices of police officers, it is impossible to determine whether and to what extent manipulative approaches such as minimization or maximization are used during suspect interviews. The fact that suspect interviews in Germany are not routinely recorded further hinders such research objectives. In a similar vein, it is difficult to determine the effectiveness of the applied interviewing practices. Although the police officers in our sample assessed themselves as rather knowledgeable with respect to suspect interviewing and skilled at detecting deception, it remains to be empirically tested whether German police officers are merely over-confident in terms of their own deception detection accuracy. Previous research shows that professionals tend to perceive themselves as rather successful lie catchers even though they are not significantly better at detecting deception than lay people (e.g., Garrido, Masip, & Herrero, 2004;Vrij & Mann, 2001).
In sum, our research suggests that none of the interviewing techniques listed in the curriculum (Conring, 2008) are taught by default to all police officers. Instead, they receive training in a wide range of different interviewing techniques, including (fragments of) the controversial Reid technique (e.g., Gudjonsson, 2003;Russano, Meissner, Narchet, & Kassin, 2005). The lack of a standardized framework and lack of routinely videotaping suspect interviews may unintentionally provide fertile ground for the use of controversial approaches (see Kassin, Kukucka, Lawson, & DeCarlo, 2014). This concern further endorses the call for a common quality standard and a common theory of suspect interviewing in Germany (Füllgrabe, 2000).
The nation-wide implementation of novel, compelling, and standardized methodslike the SUE techniquewhich adhere to the "best practice" of suspect interviewing (e.g., open-ended questions, a non-accusatory interviewing approach) and which come with a strong theoretical foundation will help to keep inefficient and unethical approaches out of the interview room.

Familiarity with/application of the SUE technique
As a second aim of this study, we examined whether the police officers are familiar with the different components of the SUE technique and which of the components they already use in their working routines. Familiarity was an important factor to study as skepticism to novel and unknown interview approaches, like the SUE technique, can be high which might prevent designated users from adopting them. However, novel approaches that are similar to the current working routine or that were previously introduced to practitioners are more likely to be met with a positive attitude. Consequently, they are more likely to get incorporated in the existing working routine. Our data showed a moderate familiarity with and use of all three SUE components. In other words, the SUE components are neither entirely new to the officers nor entirely established and applied. The partial familiarity with the SUE components can be explained by the fact that the most frequently taught interview methods at police colleges (exploratory method, determination method) contain certain structural and strategic elements that are to a certain degree comparable to some of the SUE components. Especially the determination method is similar to the Question component of the SUE technique.
Although the data indicate the police officers' partial familiarity with and application of (some of) the SUE components, none of the police officers actually reported to have learned about the SUE technique during basic or advanced training. Consequently, we assume that the officers lack knowledge on the theoretical underpinnings of these components. This knowledge is however crucial when trying to develop a deeper understanding of how the different components work together and what purpose each component fulfills for the elicitation of potential cues to deception. In an everyday working context, the lack of theoretical knowledge might not be specifically problematic. However, if one wants to master the SUE technique, it is not only important to know how to apply the components but also to understand why they have to be applied in a certain way to untap the full potential of using evidence strategically.

Assessment of the applicability of the SUE technique
The third aim of the current study was to determine how police officers assess the applicability of the SUE technique in a German context. As one prerequisite of the SUE technique is that suspects are unaware of the evidence against them before the first interview (to prevent them from adapting their statements), we asked the officers about the frequency of cases where suspects have (almost) full knowledge of the evidence held against them. Almost all officers reported that this is never or rarely the case. Only 2.6% of the officers reported that they are often confronted with this situation. Given that evidence is usually available after a crime (e.g., Wagenaar et al., 1993), this finding has positive implications for the applicability of the technique in real-life cases. Overall, this finding suggests that there seem to be no noteworthy legal hurdles to using the SUE technique in Germany.
We were further interested in the potential obstacles police officers would anticipate when using the SUE technique in their suspect interviews. The vast majority of the officers reported to not see any problems with the use of the SUE technique. Only roughly a quarter of the respondents reported to see potential obstacles of introducing the SUE technique to police practice. The content analysis revealed that the expenditure of time was the main concern of the respondents. As the Evidence component of the SUE technique requires a thorough preparation for the interview, this concern seems reasonable. However, the data of the current study show that the majority of police officers already have the tendency to preplan (many of) the themes they wanted to cover during the suspect interview. This raises the question whether the Evidence component of the SUE technique would take significantly longer than the preparation the police are already engaging in. Such concerns are not new and have also been expressed by British police officers who perceived the Cognitive Interview (CI) as too time consuming to use in the field (Kebbell, Milne, & Wagstaff, 1999). To empirically test these concerns, Rivard, Fisher, Robertson, and Hirn Mueller (2014) compared the CI with the interviewing technique, which the police officers in their sample typically used in their daily work, and found that it did not take them significantly more time to conduct the CI compared to the alternative interview. While we cannot draw any direct conclusion about how this finding might apply to the SUE technique, it shows that concerns regarding expenditure of time may be unfounded.
Two other concerns expressed by the police officers in our sample were that the technique might be too rigid and therefore (a) be incompatible with the complexity of many real-life settings (20.8%) and (b) interfere with the natural interaction between suspect and interviewer (10.4%). However, these concerns can easily be dismissed. Hartwig et al. (2014) specifically describe the three components that are part of the tactical level as "case-dependent". Accordingly, the components are meant to be suitable for many different situations and people and should not be seen as a rigid template. In other words, the developers of the SUE technique themselves do object to a rigid use of the technique and advocate for a flexible use of the tool.
Another anticipated problem conveyed by the content analysis pertains to the concern that suspects might be unwilling and/or incapable of making a statement (e.g., due to their intelligence or language barriers). However, this concern applies to all types of suspect interviews where an interviewer aims to elicit a statement from an interviewee. Given that the SUE technique has been successfully tested with children (12-14 years) implies that this concern is empirically unsubstantiated (Clemens et al., 2010). In other words, it is unlikely that a SUE interview requires a higher intelligence or better verbal abilities of the interviewee than any other suspect interviewing approach.

Implications and future directions
The findings of the current study are informative with respect to a possible implementation of the SUE technique in Germany demonstrating that there are few, if any, practical obstacles to introducing the SUE technique in Germany. Although the vast majority of police officers reported to have learned about different suspect interviewing techniques, only a minority received training on how to use potentially incriminating information during an interview. This finding is concerning as failure to efficiently and ethically use incriminating evidence, which exists in most real-life situations (e.g., Wagenaar et al., 1993), may lead to the loss of its evidentiary value and strength.
A surprising finding of this study was the relatively high number of police officers who reported to have received training in the Reid technique. As the Reid technique offers a toolbox of easily taught and applied tactics, it is possible that the absence of standardized interview protocols and training materials for suspect interviewing in Germany (Füllgrabe, 2000) might have contributed to the survival of (elements of) the technique. Based on the current data, it is reasonable to assume that there is a need for a strategic interviewing approach like the SUE technique in Germany that includes "hands-on" tactics. In addition, SUE has a strong theoretical foundation which, when accurately introduced to the police, will not only help the officers to apply the different components in the best possible way but also to understand why and how they work. Previous research has shown that combining theoretical knowledge with extensive practical training enables police officers to conduct high-quality SUE interviews leading to more correct veracity judgments (e.g., Luke et al., 2016). While this survey study was an important first step to understanding the interviewing practices and the strategic use of evidence by police officers from Schleswig-Holstein and Hamburg, future research should collect data from all 16 states to discover possible variations within the German police force.
Furthermore, it is important to examine the interviewing approaches that are used by German police officers in real-life police interviews. Although the majority of police officers in our study reported to have received training in the exploratory method to interview suspects, it is unclear how this training does translate into actual police practice. In other words, based on the data available from the current study, there is no objective way of knowing whether "best practice" guidelines are consistently followed or not.
Finally, in the context of a control-group experiment with German police officers, some should receive training with the SUE technique and their interview performance and experiences with mock suspects should be compared with a control group, which did not receive such training. Such research efforts should also aim to collect data that allow a more thorough understanding of the needs of police officers. For example, the police officers should be encouraged to share their view of the technique's effectiveness and helpfulness in in-depth interviews. Such a methodology would provide more informative and complete information than a survey.

Limitations
There are different limitations to the current study. The first limitation that we want to address is that we were only able to offer police officers a rather brief summary of the three SUE components. This was due to the fact that we did not want to present an overly long questionnaire to them which might have discouraged some officers from participating in the study. A more detailed description of the SUE technique and its components might have helped officers to understand and judge the components better.
The second limitation is that our study is based on a survey. In other words, this methodology did not allow for a more in-depth analysis of the answers, whichfor some itemswould have been of value. For example, in hindsight we would have liked to learn more about the training the respondents might have received concerning the Reid technique. Offering a separate free text field for this specific question would have allowed us to get a better understanding of the training context (e.g., whether the Reid technique was framed as a good or bad example of suspect interviewing or whether its mere existence was mentioned to the officers). However, given the purpose of this study to get an understanding of the suspect interviewing practices and strategic use of evidence by German police officers, questionnaires are an appropriate method.
Third, the phrasing of the survey question on the standardization of interviewing procedure ("To what extent do you adhere to an always identical/standardized procedure when interviewing a suspect?") was not optimal and challenges the validity of this item. While we intended to refer to the level of standardization in an interview framework (i.e., the way certain decisions are made and connected with each other), it is possible that some respondents interpreted the item differently and therefore shifted their answers toward the less standardized scale points.
Fourth, it is possible that the current study, just like any other survey study, may have suffered from selection bias. That is, those officers who are more confident about their own interviewing abilities, who do not mind (anonymously) reporting their own shortcomings, or who are more open to research and change might have been more prone to answering the survey than others.
Finally, we want to note that one has to be careful in generalizing our findings to the entire German police force given that our sample included police officers from only two German states. As each state in Germany has its own police force and autonomously establishes training content and guidelines regarding suspect interviewing, future research should systematically examine possible differences between the states.

Conclusions
Our research demonstrated that the potential for strategic evidence disclosure techniques within suspect interviewing in Germany is still untapped. Although the prerequisites for the SUE technique are fulfilled (e.g., suspects are typically unaware of the evidence against them) and police officers already receive training in interviewing approaches that are structurally similar to the SUE technique, they do not yet receive comprehensive training on how to strategically use evidence.
Our research also exposed a demand for systematic and nation-wide research into the state of suspect interviewing practices in Germany. Even though manipulative and unethical interviewing techniques like the Reid technique are prohibited by German law, we cannot say with confidence that none of its controversial elements are used by German police. Therefore, we join other researchers who call for improving the quality of interview training and practice in Germany (e.g., Hermanutz & Litzcke, 2006). Clearly, the criminal justice system is poorly served by interviewing tools that are ineffective. By intensifying the efforts to actively exchange knowledge between researchers and practitioners and incorporating scientifically solid methods (like the SUE technique) into police training and procedures, we believe it is possible to improve current practices (see Fisher, Schreiber Compo, Rivard, & Hirn, 2014 for a similar perspective).

Disclosure statement
No potential conflict of interest was reported by the authors.

Data availability statement
The dataset generated and analyzed during the current study is available from the corresponding author on reasonable request. During your basic/advanced training, did you learn about "the use of potentially incriminating information against a suspect during an interview"?

Yes/No 5
To what extent do you adhere to an always identical/ standardized procedure when interviewing a suspect?
Always "case by case" decision (1), Always standardized (5)  6 To what extent are the themes you address when interviewing a suspect preplanned or spontaneous?
All spontaneous (1), All preplanned (5) 7 To what extent is the decision on when and how to use the evidence against a suspect during an interview an analytical decision (e.g., a strategic plan that you are following) or a gut decision (e.g., a feeling that guides you)?
Pure gut decision (1), Pure analytical decision (5) 8 How well-informed do you perceive your knowledge pertaining to suspect interviewing?
very bad (1) to very good (5) 9 In your opinion, in how many of your suspect interviews (in %) are you correct about a suspect's veracity?
0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% Familiarity with/application of the SUE components This is not at all how I work (1), This is precisely how I work (5) Assessment of the applicability of the SUE technique 12 How often do you have to deal with cases where the suspect might have (almost) full knowledge of the evidence the police hold against him/her before the first interview (e.g., because his/her lawyer viewed the files beforehand)?
Never (1), Always (5) 13 Do you see any potential problems in case this technique would be applied in practice?

Yes/No
13a If yes, which? Open response format