Facts only the perpetrator could have known? A study of contamination in mock crime interrogations

Law Hum Behav. 2020 Apr;44(2):128-142. doi: 10.1037/lhb0000367. Epub 2020 Mar 12.


Objective: This paper examines contamination in interrogations: the process by which an interrogator divulges privileged information to a suspect.

Hypotheses: In Experiment 1, we predicted that mock investigators would communicate critical crime details when they interview mock suspects about a crime-and that innocent and guilty suspects alike would later produce confessions that contained these details. In Experiment 2, we hypothesized that observers who listened only to the confessions would exhibit a greater guilt bias than those who also had exposure to the eliciting interview.

Method: Experiment 1 (N = 59) used student participants in a mock crime scenario to test whether contamination is natural to communication even in the absence of external incentives. In Experiment 2, MTurk participants (N = 499) listened to audio-clips from Experiment 1 to test whether presenting observers with the full interview decreases guilt ratings for false confessors.

Results: Investigators divulged crime information to both innocent and guilty suspects, and even false confessions later included accurate details. Although Experiment 2 observers exhibited a guilt bias, exposure to the interview (not just the confession) attenuated this effect for innocent confessors.

Conclusions: The information disclosure associated with contamination is a normal cognitive process that occurs even without external incentives to secure a confession. Experiment 2 showed that seeing contamination in action may decrease judgments of guilt for innocent suspects. Interrogations should be recorded in their entirety to provide fact finders with an objective record of the source of crime details contained within narrative confessions. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Case-Control Studies
  • Crime / psychology*
  • Criminal Law*
  • Disclosure / legislation & jurisprudence*
  • Female
  • Humans
  • Interviews as Topic / methods*
  • Law Enforcement*
  • Male
  • New England
  • Students / psychology
  • Universities
  • Young Adult