In the case of Ronald Rompilla v. Jeffrey A. Beard, Secretary, Pennsylvania Department of Corrections (2004), the U.S Supreme Court ruled in favor of Rompilla, stating that his legal counsel provided ineffective assistance during sentencing for a capital offense by failing to investigate and present mitigating evidence about his background and mental health. Despite being aware that the prosecution intended to seek the death penalty based on aggravating factors, Rompilla's lawyers did not examine his prior conviction records which contained information about his troubled childhood and alcoholism - factors that could have potentially swayed jurors towards leniency. The court held this as a violation of Rompilla's Sixth Amendment right to effective legal representation.

In the dissenting opinion for Ronald Rompilla v. Jeffrey A. Beard, Justice Anthony Kennedy argued that the majority's decision to overturn Rompilla's death sentence was unjustified and set a dangerous precedent for future cases. He contended that Rompilla's defense attorneys had acted reasonably in their investigation of his background, despite not reviewing certain records related to his prior conviction which might have provided mitigating evidence during sentencing. Kennedy emphasized that these lawyers were experienced and competent professionals who made strategic decisions based on what they believed would be most beneficial for their client’s case at trial; thus, it was wrong to second-guess them with hindsight bias after the fact. Furthermore, he expressed concern about imposing an overly burdensome duty on defense counsel to investigate every possible avenue of mitigation evidence regardless of its apparent relevance or usefulness.