Attorney Robert Smith, who represents Johnny Paul Penry, said jurors were given a "hopelessly confusing instruction" when they sentenced Penry to death for killing a woman by stabbing her with a pair of scissors. Penry's lawyers say he is mentally retarded and has the mind of a 7-year-old.
The justices heard arguments in his case one day after announcing they will consider this fall whether the Constitution allows mentally retarded killers to be executed at all.
The justices gave no clues in Tuesday's argument on how they view that question. However, some expressed concern about the way jurors in Penry's case were told to consider his mental capacity in deciding whether to sentence him to death.
"That's such an odd posture; it's very awkward to say the least," said Justice Sandra Day O'Connor.
Justice David H. Souter added, "This was not a reasoned moral process, it was an irrational process."
However, Justice Antonin Scalia suggested that jurors should be able to understand the instruction. "We assume the jury is, even if the defendant is mentally deficient, that the jury is not," the justice added.
Attorney Gene C. Schaerr, arguing for Alabama in support of the prosecutors, said the instruction "gave the jury at least one clear path to a life sentence."
The Supreme Court used Penry's case in 1989 to rule that the Constitution allows the execution of killers with mental retardation. But on Monday, the justices announced they will consider that question anew.
The court said it will use the case of North Carolina death-row inmate Ernest McCarver to consider whether, under society's current standards, the Constitution's ban on "cruel and unusual punishments" bars the execution of mentally handicapped people.
McCarver's lawyers say he has retardation. The justices halted his execution early this month just hours before he was to be put to death.
Prosecutors said considerable evidence showed that McCarver did not have mental retardation, but they added that even if he did, his execution would not violate the Constitution.
It was not immediately clear how the justices' decision to hear McCarver's case this fall will affect the Texas appeal. But Smith, Penry's lawyer, said that if the Supreme Court decides people with mental retardation cannot be executed, "I would hope and believe that that decision will be applied to Penry."
Earlier this month, the justices blocked the execution of a Missouri death-row inmate said by his lawyers to have borderline retardation. Antonio Richardson had been scheduled to be put to death March 7.
Penry was on parole for rape when he was arrested in 1979 and charged with murdering Pamela Moseley Carpenter, the 22-year-old sister of former Washington Redskins kicker Mark Moseley. Carpenter was stabbed in the chest with scissors she had been using to make Halloween decorations, but was able to describe her attacker before dying.
Penry confessed, underwent two competency trials and two murder trials and twice prepared for lethal injection. He was spared most recently on Nov. 16 when the Supreme Court decided to consider his case.
The victim's brother tells CBS News Correspondent Jennifer Jones that reversing the ruling would be wrong.
"I think he should die," said Mar Moseley. "That's it he's guilty, he did it."
There have been 702 inmates executed nationwide since a Supreme Court-ordered moratorium ended in 1977. Of those, about 35 had showed evidence of mental retardation in tests, said Richard Dieter of the Death Penalty Information Center, a group critical of how capital punishment is administered.
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