Penry, 45, has the IQ of a 7-year-old, according to his lawyers, and his appeals have been the basis of historic high court decisions, first supporting the execution of the mentally retarded and then ensuring that juries have a chance to consider the issue.
In a decision Thursday, a jury in Conroe determined that Penry was competent to face a Texas jury for a third time to determine whether he should be sentenced to death or a life prison term. The punishment trial is scheduled to begin April 29.
Penry's capital murder conviction for the 1979 rape and murder of Pamela Moseley Carpenter, 22, in Livingston, Texas, stands. The Supreme Court, however, has sent the case back to Texas twice in recent years because of errors in the sentencing phase.
In 1989, the high court upheld the execution of the mentally retarded, but said the jury must be allowed to consider the issue of mental retardation in sentencing. Last year, the court ruled prosecutors had tried Penry a second time before Texas law had been changed to reflect their 1989 decision.
The jury's finding Thursday that Penry is competent to stand trial was not a surprise, according to Neil McCabe, a professor of criminal law at the South Texas College of Law in Houston, who said that issue usually relates more to mental illness.
"The issue is whether he knows enough about what's going on and understands it so that he can cooperate with his lawyer in his defense," he said. "I understand he's pretty savvy about the system."
McCabe said Penry's best hope of avoiding the death penalty maybe with a Virginia case pending before the Supreme Court because the court will probably reverse its previous stand and ban the execution of the mentally retarded.
"They are going to hold that you can't execute the mentally retarded because things have changed and now it would be considered cruel and unusual punishment," he said.
McCabe said the court doesn't usually listen to public opinion on constitutional issues but the Eighth Amendment's ban of "cruel and unusual punishment" is an exception because "it's a changing, developing standard and America changes."
The court heard oral arguments in the Virginia case Feb. 20 and a ruling is expected before the term ends in June.
Sentiment against the execution of the mentally retarded has been growing in recent years. Eighteen of the 38 states with a death penalty statute and the federal government have laws banning the practice.
The Texas Legislature passed a law last year banning execution of the mentally retarded, but Gov. Rick Perry vetoed the measure, explaining that jurors should decide the question.
Penry, who still believes in Santa Claus, according to his attorneys, has never scored higher than the low 60s on nine IQ tests. An IQ of 70 or below is considered mentally retarded, according to most experts.