Expert testimony in capital sentencing: juror responses.

The U.S. Supreme Court, in Furman v. Georgia (1972), held that the death penalty is constitutional only when applied on an individualized basis. The resultant changes in the laws in death penalty states fostered the involvement of psychiatric and psychologic expert witnesses at the sentencing phase of the trial, to testify on two major issues: (1) the mitigating factor of a defendant's abnormal mental state and (2) the aggravating factor of a defendant's potential for future violence. This study was an exploration of the responses of capital jurors to psychiatric/psychologic expert testimony during capital sentencing. The Capital Jury Project is a multi-state research effort designed to improve the understanding of the dynamics of juror decision-making in capital cases. South Carolina data (n = 214) were used to investigate the impact of expert testimony on the mitigating factor of mental illness and the aggravating factor of future dangerousness. Ordered logit regression analyses revealed significant correlations (p < .005) between the presence of a defense psychiatrist or psychologist expert witness during the sentencing phase and jurors' having the impression that the defendant was mentally disturbed. Similar analyses revealed no significant relationship between the presence of state-introduced psychiatric testimony and jurors' having the impression that the defendant, if not executed, would be violent in the future. These findings seem to contradict the view that psychiatric testimony on future dangerousness in death penalty cases has a powerful impact on jurors. The jurors in this study were significantly influenced, however, by psychiatric/psychologic testimony in the area of a defendant's mitigating mental abnormality.