In the case of Sumner, Director, Nevada Department of Prisons, et al. v. Shuman in 1986, the U.S Supreme Court ruled that a mandatory death sentence for prisoners serving life without parole who commit murder while incarcerated is unconstitutional. The court held that such a law violated the Eighth Amendment's prohibition against cruel and unusual punishment because it did not allow consideration of individual circumstances or mitigating factors before imposing capital punishment. This decision was based on an appeal by Raymond Wallace Shuman who had been automatically sentenced to death after being convicted for killing another inmate while already serving a life sentence without possibility of parole for first-degree murder committed in 1958.

In the dissenting opinion for Sumner v. Shuman, Justice Brennan argued that mandatory death sentences are unconstitutional because they do not allow for individualized consideration of mitigating circumstances. He believed that such a sentence is excessively severe and degrading punishment, which violates the Eighth Amendment's prohibition against cruel and unusual punishments. Furthermore, he contended that this ruling contradicts previous Supreme Court decisions which held that capital punishment must be based on an individual assessment of each defendant’s culpability rather than being automatically imposed without regard to personal characteristics or circumstances surrounding the crime. In his view, even if a prisoner serving life imprisonment commits murder while in prison, there should still be room for considering factors like motive or provocation before deciding on capital punishment.