In the case of Martin Horn, Commissioner, Pennsylvania Department of Corrections et al. v. George E. Banks in 2001, the United States Supreme Court was asked to consider whether a death row inmate's mental illness could be used as grounds for staying his execution. Banks had been convicted and sentenced to death for killing thirteen people in 1982 but argued that he was mentally incompetent and therefore should not be executed under the Eighth Amendment prohibition against cruel and unusual punishment. The lower courts ruled that Banks' claims were procedurally defaulted because they were not raised at state court level first before being brought up on federal habeas review; thus denying him relief from his sentence due to this procedural default rule which requires all claims to be presented at every level of appeal unless there is cause shown why it wasn't done so previously along with actual prejudice resulting from such failure or if failure would result in fundamental miscarriage of justice.

In the dissenting opinion for Martin Horn, Commissioner, Pennsylvania Department of Corrections et al. v. George E. Banks (2001), it was argued that the majority had erred in their decision to grant habeas corpus relief to Banks on his claim of ineffective assistance of counsel during sentencing proceedings. The dissenters believed that there was no reasonable probability that if Banks' trial counsel had presented additional mitigating evidence about his mental health and background at sentencing, the outcome would have been different given the gravity and number of crimes committed by him - 13 murders including five children and one former girlfriend who were killed execution-style after being lined up against a wall. They also disagreed with the majority's conclusion regarding prejudice under Strickland v Washington standard which requires showing not just potential influence but 'reasonable probability' that jury verdict could have been affected by attorney errors or omissions.