Some witnesses of crime do not want to cooperate with the police during the police investigation, and their participation is not obligatory. However, witness statements are critical to advance police investigations and deliver justice. This PhD research focuses on the promotion of cooperation during witness interviews.

Based on police interviews with crime witnesses in the Netherlands and a survey of criminal investigators in the Netherlands, Sweden and the United Kingdom, the findings indicate deficiencies in the application of evidence-based witness interviewing techniques, which may be exacerbated when witnesses are uncooperative with the police. Lack of witness cooperation was also found to be detrimental to accurate disclosure of information. Altogether, these effects call into question the validity of witness statements used in criminal investigations and proceedings. Further research, interviewing training, and policies are needed to reduce lack of witness cooperation and to secure the best witness evidence.