Congress or any state legislature may prescribe the death penalty, also known as capital punishment, for murder and other capital crimes. The Supreme Court has ruled that the death penalty is not a per se violation of the Eighth Amendment's ban on cruel and unusual punishment, but the Eighth Amendment does shape certain procedural aspects regarding when a jury may use the death penalty and how it must be carried out. Because of the Fourteenth Amendment's Due Process Clause, the Eighth Amendment applies against the states, as well as the federal government.

Eighth Amendment analysis requires that courts consider the evolving standards of decency to determine if a particular punishment constitutes a cruel or unusual punishment. When considering evolving standards of decency, courts both look for objective factors to show a change in community standards and also make independent evaluations about whether the statute in question is reasonable.

Proportionality Requirement

The U.S. Supreme Court has determined that a penalty must be proportional to the crime; otherwise, the punishment violates the Eighth Amendment's prohibition against cruel and unusual punishments. In performing its proportionality analysis, the Supreme Court looks to the following three factors: a consideration of the offense's gravity and the stringency of the penalty; a consideration of how the jurisdiction punishes its other criminals; and a consideration of how other jurisdictions punish the same crime.

In the landmark case of Coker v. Georgia, 433 U.S. 584 (1977), the Supreme Court ruled that a state cannot apply the death penalty or the crime of raping an adult woman because it violates the proportionality requirement. The Court came to this conclusion by considering objective indicia of the nation's attitude toward the death penalty in rape cases. At the time only a few states allowed for executions of convicted rapists.

Twenty-one years later, in Kennedy v. Louisiana (07-343) (2008), the Supreme Court extended its ruling in Coker, holding that the penalty is categorically unavailable for cases of child rape in which the victim lives. Because only six states in the country permitted execution as a penalty for child rape, the Supreme Court found the national consensus to hold its use in these cases as disproportionate.

Principle of Individualized Sentencing

To impose a death sentence, the jury must be guided by the particular circumstances of the criminal, and the court must have conducted an individualized sentencing process. In the 2002 Ring v. Arizona decision, the Supreme Court ruled that a jury, rather than a judge, must find an aggravating factor to exist for cases in which those factors underlie a judge's choice to impose the death penalty rather than a lesser punishment. 536 U.S. 584. An aggravating factor is any fact or circumstance that increases the culpability for a criminal act.

The Supreme Court further refined the requirement of "a finding of aggravating factors" in Brown v. Sanders. 546 U.S. 212 (2006). For cases in which an appellate court rules a sentencing factor invalid, the Court ruled that the sentence imposed becomes unconstitutional unless the jury found some other aggravating factor that encompasses the same facts and circumstances as the invalid factor.

Another 2006 cases, Kansas v. Marsh, offered yet another clarification to the principle of individualized sentencing jurisprudence. After Marsh, states may impose the death penalty for situations in which the jury finds the aggravating and mitigating factors to equally balance, without violating the principle of individualized sentencing.

Method of Execution

A legislature may prescribe the manner of execution, but the manner may not inflict unnecessary or wanton pain upon the criminal. Courts apply an "objectively intolerable" test when determining if the method of execution violates the Eighth Amendment's ban on cruel and unusual punishments.

State courts and lower federal courts have refused to strike down hanging and electrocution as impermissble methods of execution; however, the U.S. Supreme Court did not take up a method of execution case for 117 years until Baze v. Rees (07-5439) in 2008. In Baze the Supreme Court held that lethal injection did not constitute a cruel and unusual punishment. This case resolved a controversial issue in light of recent evidence that a lethal injection's three-drug combination fails to alleviate pain and prevents the criminal from signaling such pain because of paralysis inducement.

Classes of Persons Not Eligible for the Death Penalty

More recently, in Atkins v. Virginia, 536 U.S. 304 (2002), the Supreme Court determined that executing mentally retarded criminals violates the ban on "cruel and unusual punishments" because their mental handicap lessens the severity of the crime and therefore renders the extraordinary penalty of death as disproportionately severe. However, in Bobby v. Bies, the Court held that states may conduct hearings to reconsider the mental capacity of death row inmates who were labeled mentally retarded before the Court decided Atkins, because before Atkins, states had little incentive to aggressively investigate retardation claims.

In Roper v. Simmons, 543 U.S. 551 (2005), the Supreme Court invalidated the death penalty for all juvenile offenders. The majority opinion pointed to teenagers' lack of maturity and responsibility, greater vulnerability to negative influences, and incomplete character development. The Court concluded that juvenile offenders assume diminished culpability for their crimes.

For more details see the Cornell Law School Death Penalty Project.