In deciding whether a convicted murderer should be sentenced to death or receive life in prison, jurors are asked to perform a balancing test.
On one hand, they must consider evidence of the seriousness and brutality of the crime. On the other, they must weigh factors about the defendant that might somewhat excuse the killer's actions.
But what happens if jurors conclude that the so-called aggravating and mitigating evidence is equally balanced? Can the jury still return a death sentence?
In a 5-to-4 decision upholding the death penalty statute in Kansas, the US Supreme Court on Monday said that states are free to decide for themselves how jurors should weigh conflicting evidence in death penalty cases.
There is no constitutional requirement that aggravating factors presented by prosecutors must outweigh mitigating factors highlighted by defense lawyers, the high court ruled.
Instead, the US Constitution requires only a fair assessment by jurors of both aggravating and mitigating evidence before deciding whether a death sentence is the appropriate punishment.
"Weighing is not an end; it is merely a means to reaching a decision," writes Justice Clarence Thomas in the majority opinion. "The decision the jury must reach is whether life or death is the appropriate punishment."
In a dissent joined by three other justices, Justice David Souter writes that when a jury is unable to draw a clear distinction between aggravating and mitigating evidence, the Kansas law creates an impermissible tie breaker in favor of a death sentence.
"A law that requires execution when the case for aggravation has failed to convince the sentencing jury is morally absurd," Justice Souter writes. "The court's holding that the Constitution tolerates this moral irrationality defies decades of precedent aimed at eliminating freakish capital sentencing in the United States."
Given the large number of convicted individuals who have been exonerated by DNA evidence since 1989, the court's rulings should make death sentences harder, not easier to impose, when they occur under questionable circumstances, Souter writes.
"In the face of evidence of the hazards of capital prosecution, maintaining a sentencing system mandating death when the sentencer finds the evidence pro and con to be in equipoise is obtuse by any moral or social measure," he writes.
In his majority opinion, Thomas responds that DNA testing is irrelevant to the issue before the court.
"The logical consequence of the dissent's argument is that the death penalty can only be just in a system that does not permit error," Thomas writes. "Because the criminal justice system does not operate perfectly, abolition of the death penalty is the only answer to the moral dilemma the dissent poses. This court, however, does not sit as a moral authority."
He adds that "our precedents do not prohibit the states from authorizing the death penalty, even in our imperfect system. And those precedents do not empower this court to chip away at the states' prerogatives to do so on the grounds the dissent invokes today."
The case, Kansas v. Marsh, was being closely followed by a number of states with capital punishment statutes similar to the Kansas law.
Many states require that jurors may not impose a death sentence unless the jury agrees that aggravating evidence outweighs mitigating evidence.
But a handful of states – including Kansas – permit the imposition of a death sentence when mitigating evidence does not outweigh the aggravating evidence. In other words, if the weight of aggravating factors is perceived by the jury to be equal to the weight of mitigating factors, the Kansas statute permits the jury to impose a death sentence.
The Kansas Supreme Court ruled that the statute violated the Eighth Amendment's prohibition on cruel and unusual punishment. It does not allow the jury to express its reasoned moral response to the mitigating circumstances, the court ruled. The Kansas justices said the Constitution requires aggravating factors to outweigh mitigating factors.
In reversing the Kansas Supreme Court, the majority justices said that the Kansas death penalty statute satisfies constitutional safeguards. The decision stems from the case of Michael Marsh, who was convicted and sentenced to death for the June 1996 murder of Marry Ane Pusch and her 19-month-old daughter during a robbery and kidnapping attempt. Mr. Marsh allegedly shot and stabbed Pusch and then set her body on fire before fleeing the crime scene. The toddler died as a result of injuries from the fire.
Marsh told police that he went to the Pusch home to kidnap Pusch and the child and hold them for ransom, but that he panicked when Pusch arrived home early.
In addressing issues raised by the dissenting justices, Thomas writes the Kansas sentencing procedure does not create a presumption that death is the appropriate sentence for capital murder.
"Far from the abdication of duty or the inability to select an appropriate sentence..., a jury's conclusion that aggravating evidence and mitigating evidence are in equipoise is a decision for death," Thomas writes.
Such a verdict, Thomas mantains, is "indicative of the type of measured, normative process" the Constitution requires.