Date of Degree


Document Type


Degree Name





Margaret Bull Kovera

Subject Categories

Law | Psychology


Jury Decision Making, Multiple Defendant


When defendants are charged with interrelated crimes it is efficient to join their cases into a single trial; however, a defendant's right to a fair trial may be abrogated by this practice. In multiple defendant trials, jurors may be subject to target monitoring errors - an inability to accurately assign evidence to the correct defendant, much like they are prone to source monitoring errors (i.e., difficulty identifying the specific source of a memory, Johnson, Hashtroudi, & Lindsay, 1993). This research study tested whether target monitoring errors moderated the influence of joining defendants' on juror decisions by varying number of defendants, charge similarity and judicial admonitions. I predicted a linear trend of charge similarity and judicial admonitions for both evidence memory and perceived evidence strength, with a decrease in accuracy as the number of defendants increased. I also predicted fewer guilty verdicts in a single defendant trial than in multiple defendant trials. Jurors failed the manipulation check assessing jurors' memory for judicial multiple defendant admonitions. Contrary to predictions, increasing number of defendants at trial did not increase guilty verdicts or reduce evidence memory or perceived evidence strength. Charge similarity among defendants had no impact on juror verdict decisions or juror memory and recall. The presence of judicial admonitions did influence guilty verdicts or memory recall accuracy. The only moderation effect to emerge was on admonished jurors falsely "knowing" information not presented at trial was presented when viewing a similar charge trial.

Overall, no hypotheses were supported; however, limitations to this study may explain the null results. The participants' ratings of the co-defendants' guilt may not have been high enough to allow for a spillover effect of criminal inference. Moreover, the judicial admonitions may not have been specific enough to warn participants of potential memory errors. Finally, perhaps the operational definition of trial complexity was not an effective manipulation of complexity within the trial used. Thus, the lack of support for my hypotheses should be interpreted with caution.