Dateline: December, 2007, Issue 5
Attorneys make promises to the jury in opening statements about what the evidence will show. Sometimes the evidence fails to fulfill one or more of these promises.
Pyszczynski and colleagues (1981) investigated the effects of a promise made in an opening statement of a criminal trial that went unmet in the presentation of evidence. During this trial, one group of jurors were presented a defense opening statement in which testimony of an alibi witness was promised that would clearly indicate the defendant's innocence, although the alibi witness did not testify during the trial. For these jurors, the prosecuting attorney's closing argument made no reference to the fact that the defense failed to fulfill this promise. A second group of jurors was presented the same defense opening, promise and testimony, but the prosecutor's closing argument drew attention to the discrepancy between the promise and evidence (i.e., the alibi witness did not appear). A third group of jurors heard the defense opening without the promise of evidence indicating the defendant's innocence.
Making a promise in opening statement that goes unfulfilled in evidence can be persuasive to jurors. When the prosecutor failed to point out that the promise was unfulfilled, jurors acquitted the defendant more often. Interestingly, the promise had increasing impact over time on jurors' belief in the defendant's innocence; the judgments of jurors who did and did not hear the promise in opening grew further apart as the trial progressed.
This persuasive effect of making a promise in opening is nullified, however, when an opposing attorney points out to jurors in closing that the promise went unfulfilled. When the prosecutor alerted the jury that the defense had made a false claim about the evidence in the opening statement, jurors became less sympathetic to the defendant in their verdicts.
Source Pyszczynski, T. A., Greenberg, J., Mack, D. & Wrightsman, L. S. (1981). Opening statements in a jury trial: The effect of promising more than the evidence will show. Journal of Applied Social Psychology, 11, pp. 434-444.