The U.S. Supreme Court case Wainwright v. Witt, 1984, centered around the issue of jury selection in capital punishment cases. The defendant, Johnny Paul Witt was convicted and sentenced to death for first-degree murder by a Florida court. On appeal, he argued that his Sixth Amendment rights were violated because one potential juror was excused due to her personal beliefs against the death penalty without determining if those views would prevent or substantially impair her duties as a juror in accordance with law. The Supreme Court ruled 7-2 in favor of Wainwright (the Secretary of Florida Department of Corrections), stating that it is not necessary for jurors' views on capital punishment to be proven beyond doubt before they can be excluded from serving on a jury; instead "substantial impairment" standard should apply when assessing whether prospective jurors could carry out their responsibilities impartially despite their personal beliefs about the death penalty. This decision clarified previous rulings regarding juries and capital punishment and set an important precedent concerning how courts handle potential bias among jurors related to this contentious issue.

In the dissenting opinion of Wainwright v. Witt, Justice Thurgood Marshall argued that the majority's decision to allow for broader discretion in excluding jurors who express doubts about capital punishment undermines a defendant's right to an impartial jury. He contended that this ruling would lead to juries biased in favor of conviction and death sentences because it allows potential jurors with even slight reservations about the death penalty to be excluded from service. Furthermore, he criticized the majority for failing to provide clear guidance on how courts should determine whether a juror’s views on capital punishment would “substantially impair” their duties, leading potentially inconsistent applications across different jurisdictions. Lastly, he expressed concern that such discretionary power could disproportionately exclude certain demographic groups opposed or skeptical towards capital punishments thereby undermining representativeness and fairness of jury composition.