WASHINGTON -- Should juvenile convicts be spared the death penalty, no matter how heinous their crimes? A sizable minority of justices on the U.S. Supreme Court says yes.

In a recent dissent, four justices argued that, in all circumstances, the execution of a convict under the age of 18 at the time he committed murder is unconstitutional. Their reasoning: Given their youth, juvenile offenders aren't as morally responsible as adults. Juveniles lack "the same capacity [as adults] to control their conduct and think in long-range terms," they wrote.

Thus, according to the justices, it is never permissible to execute someone who committed a crime while under the age of 18. The New York Times agreed, calling the execution of juvenile offenders a disgrace.

One wonders what they would say today. Two days after the court opinion was issued (and a few hours after the Times editorial was finalized for publication), John Allen Muhammad and Lee Boyd Malvo were arrested. It appears that both will be charged with multiple counts of murder relating to the string of sniper homicides in Maryland, Virginia and Washington.

The initial evidence gathered by the police makes it clear that the sniper attacks were chillingly premeditated and deliberate. The sniper had a tripod and scope for firing the rifle. The car Mr. Muhammad and Mr. Malvo were driving had been modified to allow the sniper to lie down in the trunk and shoot his victims through a hole in the back of the car, making escape that much easier.

In short, the sniper hunted human beings as if they were deer in a forest, with as much care and forethought as a military battle planner.

Now Mr. Muhammad and Mr. Malvo are innocent until proved guilty. But let's assume the two are convicted of these horrendous crimes. The initial assumption of investigators appeared to be that Mr. Muhammad was the shooter and Mr. Malvo drove the getaway car. But legally, the getaway driver for a serial murderer is as guilty of the crime as the shooter himself. If the driver were 25 years old, many juries likely would sentence him to death, even though his role was merely that of an accomplice.

Still, the driver's somewhat lesser role in the crime does make it possible that a jury might show mercy and recommend that he not be sentenced to death. And that recommendation is made more likely by virtue of Mr. Malvo's youth -- if he is found guilty, a jury may not want to sentence to death a 17-year-old accomplice.

But let's turn the picture around. What if the evidence proves that Mr. Malvo was the shooter or, as some investigators believe, that he and Mr. Muhammad took turns hunting humans?

What if it was a 17-year-old who planned and executed each killing alone? Surely a jury wouldn't decline to impose the death penalty simply because he is several months short of his 18th birthday. To do so would mean drawing an arbitrary bright line between the acts of an individual who is 17 years and 6 months old and one who is 18.

Critics reply that there are many instances in which the law draws bright lines based upon age. Yet it's wrong to think that only with the maturity necessary to drive carefully, drink responsibly and vote intelligently does one come to understand that killing another human being is wrong. That kind of understanding comes at a much younger age.

Besides, we determine the guilt or innocence of any defendant individually. Laws governing driving, drinking and voting represent gross generalizations -- appropriate in making broad public policy but utterly inconsistent with our concept of individual criminal responsibility.

The absurdity of the position taken by the court dissenters is only heightened by the arrests made in the sniper case. Their reasoning boils down to this: A juvenile should never be punished in proportion to his crime because he always lacks culpable moral responsibility. But if the evidence at Mr. Malvo's trial proves what some investigators suspect, there can be little doubt as to moral culpability.

Either as driver or shooter, Mr. Malvo is accused of acting as a knowing participant in a string of cold-blooded murders. It makes no sense to say that such conduct is categorically ineligible for the death penalty.

Paul Rosenzweig, an adjunct professor at the George Mason University School of Law, is a senior legal research fellow at the Heritage Foundation in Washington.