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When eyewitnesses talk to each other after witnessing a crime, they can contaminate each other’s memory. However, laboratory research shows that collaborative interviewing can also result in correction of mistakes and retrieval of more new information. The aim of this study is to examine whether these laboratory findings would generalise to real police interviews in The Netherlands. Because little is known about which interviewing techniques Dutch police detectives use, the secondary aim was to examine how Dutch detectives approach individual and collaborative eyewitness interviews.

In a field study, witnesses of serious incidents (e.g. police shooting) were interviewed individually and then collaboratively by real investigators, resulting in 15 interviews of 1–2 h each from five witness pairs (5,534 details in total). Transcripts were coded for detail type, forensic relevance, verifiability, retrieval strategies and interviewing techniques. Results were described using both quantitative descriptive data and a qualitative analysis of interview excerpts.

On average, collaborative interviews resulted in 131 new details, over half of which were considered highly relevant to the police investigation. Interview excerpts demonstrated how content-focused retrieval strategies (acknowledgements, repetitions, restatements, elaborations) can elicit new and highly relevant details. Interviewers mostly asked clarifying questions and equal numbers of open, closed and yes/no questions, but rarely allowed for uninterrupted free recall. Interviewers asked a higher proportion of open questions during collaborative interviews than during individual interviews.

Limitations included the small sample size and lack of a control condition.

To the best of the authors’ knowledge, this paper is the first to investigate the effectiveness and feasibility of the Collaborative Eyewitness Interview in real-world settings.