Witnesses' failure to detect covert manipulations in their written statements

Law enforcement agencies and legal professionals often have to rely on witness statements. Undetected errors in witnesses' statements, however, could impede the accurate reconstruction of a crime and lead to the incrimination of innocent suspects. Here, we examined whether witnesses can detect manipulations in their written statements. We expect that writing a statement could provide a good means for discrimination between what is truly recalled and what is an error. This is because writing allows to monitor and control the previously produced information. In 3 experiments, participants watched a mock crime film and subsequently provided a written statement of what they had witnessed. Following a delay of several minutes (Experiment 1), 48hr (Experiment 2), or 1month (Experiment 3), participants were exposed to and interviewed about their testimony. Unknown to them, they were confronted with statements, which included 4 secretly manipulated details. Participants' missed a substantial number of manipulations in their written statements. Importantly, the detection rates varied as a function of delay (Experiments 1 and 2: 74-89%; Experiment 3: 36%-52%). Detection rates also varied as a function of the type of details that were manipulated. Our findings indicate that writing a statement comes with limited benefits in witnesses' ability to detect errors in their statements.