RENO, Nev. (AP) — The American Bar Association wants the Nevada Supreme Court to rule that people suffering from severe mental illness should be ineligible for the death penalty.

The national group of lawyers and legal scholars made the argument in joining an appeal challenging the death sentence of a man it says was mentally ill when he was convicted of the 1998 hatchet slaying of a campus police officer.

Siaosi Vanisi was found guilty of murder in the death of University of Nevada, Reno police Sgt. George Sullivan while he was sitting in his cruiser.

The native Tongan also was also convicted of robbing a convenience store using Sullivan's service revolver before he was arrested during a standoff with a SWAT team in Salt Lake City.

Vanisi's lawyers filed motions to withdraw from the case during his initial trial partly because he refused to cooperate with their efforts to prove he was incompetent.

One lawyer told the judge in chambers that Vanisi acknowledged killing Sullivan but wanted to blame someone else. The lawyer said that put his defense team in the unethical position of allowing Vanisi to perjure himself. The judge refused their request to withdraw and found Vanisi competent.

Vanisi told a judge earlier this year he opposes arguing for a reduced sentence because he doesn't want to spend his life in prison. Instead, he wants a new trial in federal court despite the overwhelming evidence used to convict him.

The bar association says it's a prime example of why severely mentally ill people shouldn't be subject to execution.

"Neither retribution nor deterrence is served by executing those whose perceptions of reality, logical reasoning and ability to exercise rational judgment are significantly impaired at the time of the crime," attorney Richard Shonfeld wrote in the ABA's brief filed Thursday.

The latest appeal filed on Vanisi's behalf said he was "washing himself in his own urine," ''dancing naked," ''talking gibberish" and "attempting to sabotage his defense team" before his trial.

Washoe County Deputy District Attorney Joseph Plater has said at a previous hearing that "severe mental illness as a matter of law has never been deemed a condition that renders one ineligible for the death penalty."

Defendants can claim innocence by reason of insanity under Nevada law if they can prove they couldn't distinguish between right and wrong or otherwise didn't understand what they were doing as a result of a mental disease.

"A mental health illness or disorder could be anything from bipolar disorder or schizophrenia to an excessive compulsive disorder like constantly washing your hands," Chief Deputy District Attorney Jennifer Noble said Tuesday. "Mental illness does not equate to insanity."