CAMDEN, NJ - Marvin Lister told a doctor that he was hearing voices the morning he stomped his frail, elderly cell mate to death in the Camden County jail. In a barely coherent statement, he called one of the voices a half-brother named Mo.

"Mo told me to do it," Lister said, according to the doctor's report. "I felt as big as Shaquille O'Neal. I'm the Tasmanian Devil."

State Superior Court Judge Irvin J. Snyder read sections of the report aloud in court yesterday, noting that the doctor found that Lister was "acutely psychotic" in 2004 when Lister killed Joel Seidel, a 65-year-old Cherry Hill man jailed for violating a restraining order.

Snyder ruled yesterday that Lister was not guilty of murder by reason of insanity and ordered him held in a mental institution indefinitely. The ruling will bring little change to Lister's life. The 38-year-old has been confined to institutions for more than a decade because of violent behavior attributed to paranoid schizophrenia and substance abuse.

The slaying led to changes at the Camden County jail and caused a debate in the county justice system about how to handle mentally ill inmates.

Seidel had a mental illness that could make him a nuisance, but he was never violent, friends said. He was jailed for violating an order that barred him from contact with his former wife and his daughter. He could have been released for a $150 bond.

Instead, he was put in a cell with Lister, who was being held there after he punched a doctor and raped another patient at Ancora Psychiatric Hospital in Winslow Township. Lister was found not guilty by reason of insanity on the rape and assault charges yesterday as well. The doctor who evaluated him found that Lister didn't know what he was doing was wrong, and "he thought he was acting in self-defense" when he attacked Seidel.

Seidel suffered multiple skull fractures and broken ribs, a torn heart, and a lacerated liver. His family is suing the jail.

"It's truly a case study of what bad can happen in the prison system... and how it just doesn't protect vulnerable, mentally ill people," said Tom Kline, the family's attorney. "It's a crying shame."

Three corrections officers were disciplined after Seidel's death. Prosecutors found that officers had not checked the cells in the psychiatric unit for about 50 minutes, and that a log sheet had been changed after the beating.

Months after Seidel's death, the jail hired 23 more officers and, later, instituted more training in handling mentally ill inmates. The jail also has redoubled efforts to keep inmates segregated so a maximum-security prisoner like Lister can't be housed with a minimum-security prisoner like Seidel.

Late last year, the county sponsored a forum for police departments on how to deal with the mentally ill without sending them to an overcrowded jail. The charges against Lister languished for two years until he was found competent enough to comprehend the court procedures. He eventually told the doctor that he understood that "the prosecutor is not helping me," and described his attorney as "a nice person who sends a doctor to see me."