One of the central justifications for the use of compensated criminal witnesses is the idea that juries can evaluate informant credibility in ways that lead to fair and reliable outcomes. Specifically, the Supreme Court held that rewarding criminals for testimony is constitutional, relying in part on the procedural protections of discovery, cross-examination, and jury instructions. The idea is that the government can constitutionally reward its witnesses as long as the defense knows about it and the jury is properly instructed.
Recent psychological research throws some doubt on this idea. Dr. Jeff Neuschatz and a number of other psychologists published the following paper: The Effects of Accomplice Witnesses and Jailhouse Informants on Jury Decision Making, Law & Human Behavior 32 (2008): 137-149. They concluded that jurors who were told that a witness was getting a deal (and therefore had an incentive to lie) were just as likely to convict as jurors who didn’t know that the witness was being compensated. Moreover, the bare fact that an informant said there was a confession made the jury more likely to convict. From the article:
First, both college and community samples demonstrated that conviction rates were unaffected by the explicit provision of information indicating that the witness received an incentive to testify. Second, and consistent with the research on confession evidence in the courtroom, the presence of a confession, albeit a secondary confession, had a significant influence on mock juror conviction rates. More specifically, in every witness typeand across both college and community samples, mock jurors convicted significantly more often when there was a secondary confession provided by a cooperating witness than when no such witness had testified….
Even though the witness in the incentive condition had an enormous motivation to fabricate evidence (having been provided a situational incentive to testify), jurors appeared to ignore this information and render verdicts that were not significantly different across the Incentive and No Incentive conditions. The participants may not have recognized or considered the impact that an incentive might have on behavior and/or the willingness to provide accurate and truthful information. Furthermore, participants did not have significantly different ratings of truthfulness or trustworthiness across the Incentive and No Incentive conditions.
This is an important finding. The system assumes that jurors who are told that an informant is getting a deal will be less likely to believe the informant and less likely to convict. This study suggests not only that this isn’t so, but that just having a criminal informant testify to a confession significantly enhances the likelihood of a conviction.