Why did the Supreme Court consider death sentences arbitrary in Furman v. Georgia?

In Furman v. Georgia (1972), the U.S. Supreme Court ruled 5–4 that the death penalty violated the Eighth Amendment’s prohibition against "cruel and unusual punishment" because it was applied in an arbitrary and discriminatory manner.12

While Justices Thurgood Marshall and William Brennan argued that capital punishment was unconstitutional in all circumstances, the remaining three justices in the majority—Potter Stewart, Byron White, and William O. Douglas—focused on the lack of fairness in its administration. They concluded that the legal systems in place allowed the death penalty to be imposed so "wantonly and so freakishly" that it functioned essentially at random. Justice Potter Stewart famously characterized this inconsistency by stating that being sentenced to death was "cruel and unusual in the same way being struck by lightning is cruel and unusual".23

Furthermore, the Court recognized that this arbitrariness was often compounded by discrimination, as the penalty was disproportionately applied to poor, mentally ill, and Black defendants. This ruling effectively nullified existing death penalty statutes and forced states to develop more consistent, guided sentencing procedures.23