Potential consequence: statements that are incomplete or even incorrect, and a real risk of wrongful case outcomes. 'Tailored interviewing and rights protection are crucial for this group in particular,' says Kranendonk.
About one in three suspects has a mild intellectual disability (MID)
The study estimates that roughly one in three suspects interviewed by police has a MID. Yet this often goes unnoticed, partly due to suspects appearing “streetwise” or overly compliant. Basic-level police interviewers are often not sufficiently trained to recognize signs of a MID. 'In 44% of the cases we studied, there were clear signs of a MID, yet the interviewers had no prior awareness of the suspect’s vulnerability,' Kranendonk explains. 'A suspect with a MID won’t always say they don’t understand something. Their compliant behaviour actually makes it harder to see they need support.'
Failure to recognize MID undermines legal protection
Not recognizing a MID can seriously harm a suspect’s legal position. These suspects often struggle to understand their rights, answer questions accurately, or provide complete information. They’re also more susceptible to suggestive questions and more likely to say “yes” even when it’s not accurate. Without adaptations to the interview process, their statements may be incorrect—sometimes even leading to false confessions. Necessary support might also be missed. 'If you don’t understand what’s being asked of you, you can’t give a proper statement. That undermines the criminal justice process,' says Kranendonk.
Trained interviewers recognize more and adapt better
Interviewers who’ve received additional training and are aware that a suspect has a MID are better able to respond to their needs. They use simpler language, avoid confrontational techniques, and take time to build rapport. They’re also more likely to ask open-ended questions and check the suspect’s understanding.
'An open, attentive attitude and verifying and summarising information help not only suspects with a MID, but improve the quality of interviews overall,' says Kranendonk. These factors increase the likelihood of reliable, case-relevant information—even when the suspect does not have a MID.
Findings directly applicable in practice
The study offers practical tools for identifying suspects with a MID and tailoring the interview approach to their needs. These insights can be immediately applied in police education and training. This is especially important given the high number of MID suspects in common criminal cases, and the fact that the basic police training program has been shortened - leaving officers potentially less prepared to work with this group. 'To interview suspects with a MID in a fair and effective way, we need to invest in awareness and training. Especially now that interview training is showing such positive effects. This benefits both the suspect and the integrity of the justice system,' Kranendonk stresses.
Benchmarked against international standards
By comparing Dutch interviewing practices to international standards like the Méndez Principles on Effective Interviewing for Investigations and Information Gathering, this study contributes to the further professionalization of (inter)national interviewing practices. The findings are relevant for law enforcement, the criminal justice process, policymakers and scholars, and help promote a fair justice system that protects even the most vulnerable suspects.
Study based on real-life interviews and expert input
The research combines a literature review with 53 interviews with MID experts, police detectives, prosecutors and defence lawyers. It also includes analysis of 92 video recordings of police interviews—covering both common and more serious criminal cases.
These reveal how interviewers detect signs of a MID, what kinds of questions and techniques they use, and how these affect the quality and reliability of suspect statements.
Kranendonk will defend her PhD based on this research on 26 June at Vrije Universiteit Amsterdam. She is currently a researcher at the Netherlands Institute for the Study of Crime and Law Enforcement and the Dutch Police Academy.