In the case of Paul Delo, Superintendent, Potosi Correctional Center v. Frederick Lashley (1992), the U.S Supreme Court addressed an appeal from a death row inmate who claimed that his constitutional rights were violated during sentencing because he was not allowed to present mitigating evidence. The court ruled in favor of Delo and upheld Lashley's death sentence on the grounds that any error made by excluding such evidence was harmless beyond a reasonable doubt. The decision affirmed that while defendants have a right to present mitigating circumstances during sentencing in capital cases under the Eighth Amendment, this does not necessarily mean all types of evidence must be admitted without restrictions or limitations.

In the dissenting opinion for Paul Delo, Superintendent, Potosi Correctional Center v. Frederick Lashley (1992), Justice Blackmun argued that the majority's decision to deny habeas corpus relief was flawed due to their failure to consider whether or not Lashley had received effective assistance of counsel during his trial. He pointed out that Lashley's defense attorney failed to present any mitigating evidence during sentencing despite there being a wealth of such information available. This included details about Lashley’s troubled upbringing and mental health issues - factors which could have potentially swayed the jury towards a lesser sentence than death. Furthermore, he criticized the court for ignoring established precedent regarding ineffective assistance claims in capital cases by focusing on individual errors rather than considering cumulative impact of multiple mistakes made by defense counsel throughout proceedings.