Blue Line

A better way to disclose evidence

August 18, 2016
By Kerry G. Watkins

2104 words – MR

A better way to disclose evidence

by Kerry G. Watkins

Most police training courses and manuals offer little or no guidance on when and how to disclose evidence to a suspect during an investigative interview.


Some texts recommend that an investigator should confront a suspect with the evidence at the start of an interview (<Yeschke, 1997>), while others suggest it should be disclosed relatively early in the process to overcome denials of responsibility (). However, none of these sources provide any scientific evidence to support their recommendations.

Moreover, while investigators will frequently have some form of evidence they could disclose to a suspect if they chose to, few have been trained on when and how to disclose it to maximize its strategic value ().

Research indicates, and the author’s personal experience confirms, that many investigators disclose all or much of their evidence at the start of an interview, particularly where they feel they have a strong case. This is done, presumably, in the hope that it will lead to a spontaneous admission or confession. However, best estimates are that suspects confess perhaps 50 per cent of the time, and possibly far less often (<Gudjonsson, 2003; St-Yves, 2014>). That being the case, what impact does early disclosure have on a suspect interview, and is it the best way to proceed?

Disclosing evidence at the beginning or early stages of an interview can actually impair an investigation in several ways.

First, early disclosure shows an investigator’s hand. Suspects who decide to confess know the evidence against them and can tailor their statement to it, constructing a false yet plausible explanation for events which may now be difficult for an investigator to disprove ().

Second, the early disclosure of any evidence (not just “hold back”) makes it difficult for an investigator to corroborate a true admission or confession with reference to evidence withheld from the suspect until they give a statement.

Third, early disclosure deprives an investigator of the ability to use evidence strategically to encourage a suspect to produce a detailed account of their involvement in the offence, and to subsequently challenge that account where it is inconsistent, either internally or with other evidence.

Investigators have to decide on a case by case basis if, when and how they will introduce evidence during a suspect interview. However, contemporary police culture has come to recognize the need for police practices to be “evidence-based;” that is, to be informed by scientific research about what is and is not effective.

There is broad agreement in the research literature that disclosing evidence later in a suspect interview is generally more beneficial. The later disclosure has been found to: increase the extent to which guilty subjects offer critical disclosures of information; result in more comprehensive and more self-incriminating accounts; increase the likelihood of a suspect confessing (); and produce more pronounced inconsistencies in the statements of lying suspects relative to those telling the truth ().

If we accept that it is generally better to disclose evidence later, the next question becomes how an investigator should introduce evidence to maximize its value. There are a number of arguments to be made for doing so incrementally; that is, progressing from the weakest evidence to the strongest.

First, a suspect may be more likely to respond to weaker evidence where they perceive an opportunity to “explain it away,” than to stronger evidence, which may simply cause them to stop talking.

Second, moving from weaker to stronger evidence allows an investigator to progressively “build” the strength of the evidence against the suspect both factually and psychologically. This is particularly important because a suspect’s perception of the strength of the case against them has been identified as the single most important factor in their decision to confess (<Bull, 2014; St-Yves et al., 2014; Fahsing, et al., 2009>).

Third, disclosing evidence later in an interview imposes a higher “cognitive load” (i.e., it is more mentally demanding) on a lying suspect than on one telling the truth, which has been shown to result in liars generating more inconsistencies in their statements than truth tellers ().

With respect to the last point, investigators can use both questioning and disclosure tactics during an interview to provide a lying suspect with the greatest opportunity to generate inconsistencies. Instead of using many direct questions early in the interview process – something many investigators do – the interviewer should use what is referred to as a “question funnel.”

Starting at the top of the funnel, the interviewer poses a series of open questions (e.g., tell/explain/describe), which invite the suspect to provide a free account about pertinent actions or events. As the funnel gradually narrows, the interviewer begins to ask more direct questions (e.g., who/what/where/when/why/how) about the evidence they hold.

The questioner might start by asking the suspect to describe the various places visited on the day in question. Were they at a particular gas station? If so, did they go inside? Where did they go? To the cashier’s counter? Did they touch it? – and so on.

Research indicates that investigators who withheld evidence until later in suspect interviews and used a funnel type questioning approach significantly improved their ability to make accurate judgments about the truth of a suspect’s statement on the basis of inconsistencies than investigators who do not take this approach ().

Once an investigator decides to disclose evidence to a suspect, careful consideration should be given on how to present it to maximize its strategic value. has developed a simple evidence framing matrix for this purpose which has two different dimensions: source of and specificity of evidence.

chart in word doc From:

The source of evidence varies along a continuum from weak to strong, and refers to how the investigator knows what they know. For example, if surveillance video showed the suspect inside the Quickie Mart at Main Street and First Avenue at 10am last Tuesday, the investigator could “frame” that evidence when they disclose it to the suspect.

For example, “We have video of you inside the Quickie Mart at Main and First Avenue at 10am last Tuesday” is a strong disclosure of the source of the evidence. Instead, the investigator could say “We have information that you were at the Quickie Mart at Main Street and First Avenue last week,” which is a weaker disclosure of the source.

The second dimension of the evidence framing matrix involves the specificity of the evidence — in other words, exactly what the investigator knows. The specificity ranges along a continuum from low to high. For example, the interviewer could say, “I know you were at the Quickie Mart last week at Main Street and First Avenue,” which is a high degree of specificity – or “I know you were in Etobicoke last week” (the location of the Quickie Mart), which is a lower degree of specificity.

Suspects first presented with evidence framed in the weakest, least specific manner possible (i.e., quadrant A) may decide to revise their statement to include the information being disclosed, while still attempting to deny more incriminating elements. For example, if the investigator said “I have information that you were in Etobicoke last week,” the suspect may revise their account to include that fact but still try to conceal that they went to the Quickie Mart at Main and First.

If the investigator then presents more specific information about the evidence, the suspect may now be forced to again revise their account. By framing evidence generally at first, and then disclosing it in an incrementally more specific manner, an investigator can maximize its strategic value.

When disclosing evidence an investigator should gradually reveal increasing strength and precision (moving from quadrant A to B, C and finally D). Research shows this tactic can lead a subject to revise their statement to fit more closely with the evidence as it is revealed. Moreover, this approach appears to be relatively resistant to suspect countermeasures ().

In summary, although there will always be some exceptions, research suggests that it is generally better to disclose evidence later in suspect interviews rather than earlier; and when disclosing it, to progress from the weakest to the strongest, rather than disclosing the strongest evidence at the start.

As the old saying goes – “good things come to those who wait.” In the case of suspect interviews, science suggests that good things may come to investigators who hold the evidence close to their chests, at least until they carefully consider when and how it is best disclosed.


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Kerry Watkins, B.A. (Hons.), M.A., LL.M. has spent most of his almost 30 years with Toronto police in specialized units investigating offences such as corporate fraud, police corruption and homicide. He has conducted thousands of investigative interviews and currently works in the police education and training field. He is the primary author of (a 3rd Ed. is coming next year).