A defendant can avoid the state's death penalty if only one juror believes the suspect has shown he or she is mentally retarded, the state Supreme Court ruled Monday.

The 4-2 decision by New Jersey's highest court clarified an October decision in which the same court decided prosecutors no longer have to prove a defendant is mentally fit, shifting that burden to defendants.

That initial ruling aligned New Jersey with most other states. It likened a claim of mental retardation to a claim of insanity, which is considered an "affirmative defense."

The rulings stem from the case of Porfirio Jimenez, a Honduran day laborer charged with sexually assaulting a 10-year-old boy and killing him in 2001. Jimenez's lawyers claimed he was mentally retarded, with an IQ of 68.

The public defender's office, which is representing Jimenez and wanted the issue of proving mental retardation addressed before he went to trial, was gratified by Monday's ruling, said Stephen W. Kirsch, assistant deputy public defender.

"It certainly is easier for any party to carry a burden of proof if they have to convince only one juror as opposed to 12," Kirsch said.

The state attorney general's office, which asserted that the death penalty should only be barred when the jury unanimously finds that a defendant is mentally retarded, said it was disappointed.

"We believe that any party in a criminal proceeding in New Jersey who bears the burden of proof on a particular issue has always had to prove the issue to the satisfaction of a unanimous jury," office spokesman David Wald said.

The ruling is another blow to death penalty supporters in New Jersey, where the Legislature is considering a bill that would abolish it.

New Jersey reinstated the death penalty in 1982 but hasn't executed anyone since 1963. The Legislature imposed an execution moratorium in December 2005 when it formed a commission to study the death penalty.

The Jimenez rulings are reactions to a 2002 U.S. Supreme Court ruling that declared executing mentally retarded criminals to be a violation of the Constitution's ban on cruel and unusual punishment. The ruling said states could decide whether the burden of proof about a defendant's mental status lies with the prosecution or defense.