In the 1988 case Lockhart v. Nelson, Johnny Lee Nelson was convicted of first-degree murder and sentenced to life imprisonment without parole by an Arkansas court. The Supreme Court had to decide whether evidence of prior crimes could be used in a sentencing hearing, even if it would not have been admissible during the trial itself. The Court ruled that such evidence is indeed permissible under certain circumstances, as long as it meets specific criteria for relevance and reliability. In this particular case, they found that the lower courts did not err in admitting testimony about Nelson's previous violent behavior towards his victim because it helped establish a pattern of conduct relevant to determining his sentence.

In the dissenting opinion for Lockhart v. Nelson, Justice Thurgood Marshall argued that the majority's decision to uphold Johnny Lee Nelson's conviction despite evidence of his mental incapacity was a departure from established legal precedent. He contended that this ruling ignored previous Supreme Court decisions which held that defendants must be able to understand and participate in their own defense in order to stand trial. Justice Marshall also criticized the majority for failing to consider whether Arkansas' standard for determining competency - which required proof of insanity beyond a reasonable doubt - was constitutionally sound. In his view, this high burden of proof could potentially result in mentally ill individuals being unjustly convicted because they were unable to effectively defend themselves.