Two experiments examined two potential safeguards intended to protect accused persons against unreliable testimony from cooperating witnesses. Participants in both experiments read a trial transcript where secondary confession evidence was presented from either a jailhouse informant (Experiment 1 and 2) or an accomplice witness (Experiment 2). In Experiment 1, testimony history was manipulated so that participants were informed that the jailhouse informant had testified as an informant in 0, 5, or 20 previous cases. In Experiment 2, participants were exposed to an expert who testified about the unreliable nature of testimony from cooperating witnesses. The results of both experiments demonstrated that participants who were exposed to secondary confession evidence were significantly more likely to vote guilty than were participants in the no secondary confession control group. Contrary to expectations, the percentage of guilty verdicts did not vary with incentive, testimony history, or expert testimony. Explanations for these results are discussed, as are the practical challenges of using testimony from cooperating witnesses.
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Although the published version of the Neuschatz et al. (2008) study does not provide the modal response in its reporting of data, the current researchers obtained the full data set from the original study.
We did not use the full factorial with a no witness condition, because there is no testimony if there is no witness. In other words, it would make no sense to have a condition which states a non-existent witness has testified, say, 20 times in the past in similar conditions.
As was the case in Experiment 1, all analyses were conducted with all participants included and with only the participants who remembered the incentive. Because there were no differences in the pattern of the result, we report the analyses that included all participants.
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Since, to our knowledge, the effects of the testimony history of witnesses have never been tested before, it was unclear whether the manipulation would be powerful enough to have the intended effect. To test this, we asked 60 participants, from the same source as the main experiment, how many times an informant would have to testify before the witness no longer would be credible. More specifically, they were given the following summary and question:
A jailhouse informant is someone who is in jail and comes forward to authorities claiming to have information on a case other than their own. Sometimes this information is a confession that the jailhouse informant claims to have overheard from a fellow inmate. The authorities may give this jailhouse informant an incentive, such as time off of their jail sentence, to come forward and testify in a trial about this confession they have overheard. Some jailhouse informants of this sort have testified multiple times in different cases, each time coming forward with a confession they overheard from a fellow inmate. How many times would an informant have to testify before they were no longer a credible witness?
After reading this paragraph, respondents were asked to complete this statement: Jailhouse informants, receiving an incentive, who have testified in _____ previous cases should probably not be believed. The response options for this question were: any, 3, 5, 10, and 20. The modal response was any (50 %), and 82 % of the respondents chose either any or 3. Only 1 person out of 60 respondents indicated that 20 previous times testifying would not affect the credibility of the witness. Given the responses to the survey, we believed that our manipulation of testimony history was indeed strong enough.
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Neuschatz, J.S., Wilkinson, M.L., Goodsell, C.A. et al. Secondary Confessions, Expert Testimony, and Unreliable Testimony. J Police Crim Psych 27, 179–192 (2012). https://doi.org/10.1007/s11896-012-9102-x
- Jailhouse informants
- Accomplice witness
- Expert testimony