Gary Alvord, the Florida prison inmate who lived on death row longer than anyone else in America, has died of natural causes.The 66-year-old murderer died Sunday at Union Correctional Institution, nearly 40 years after he strangled to death three women in Tampa.Ultimately it was a brain tumor, not the electric chair or a lethal injection needle, that claimed Alvord's life, his attorneys said. In recent years, he had also battled lung cancer."Gary is a product of a sick system," said attorney Bill Sheppard of Jacksonville, who represented Alvord for most of the four decades he was on death row. "He was a living example of why we should not have a death penalty."Alvord was convicted and sentenced to death for the murders of Ann Herrmann, 36, her daughter, Lynn Herrmann, 18, and Ann's mother, Georgia Tully, 53. The three were found dead June 18, 1973, in a home off N Florida Avenue in Tampa. Lynn Herrmann was also raped.A surviving member of the Herrmann family did not return a call for comment Tuesday.Gov. Bob Graham twice signed death warrants for Alvord, in 1981 and 1984. But the execution never happened. The reason: Alvord was too crazy to be killed.Born in Michigan in 1947, Alvord was plagued by delusions and disordered thoughts that doctors attributed to paranoid schizophrenia and antisocial personality disorder. The law forbids the execution of anyone with such a mental condition.In 1967, he was jailed on charges that he raped a 10-year-old girl. Three years later, a jury found him not guilty by reason of insanity and he was sent back to a state mental hospital.In January 1973, he escaped. He surfaced in Tampa, where he quickly befriended several people, found a girlfriend, and moved into her Davis Islands apartment. He became a regular at the Guys and Dolls Billiard Hall at 1120 W Kennedy Blvd., where he met the owner, Ann Herrmann.One day, a man Alvord knew bickered with Herrmann about the price of a pool game. A witness later heard Alvord confront her. "Usually when somebody rips off my friends, I kill them," he said.Alvord later confessed to the murders to his girlfriend. He was arrested after fleeing to Michigan and convicted and sentenced to death in 1974.In the late 1970s when Florida leaders were working to resume executions, Alvord was among half a dozen inmates considered. But his mental condition led psychiatrists to conclude that he did not understand his punishment.In 1984, he was sent to a state hospital in Chattahoochee to be restored to competence. But doctors there refused to treat him, citing the ethical dilemma of making a patient well just so that he could be killed. He was quietly returned to death row in 1987 and remained there ever since. His final appeal expired in 1998."I would love for the state of Florida to tell us how much money they wasted trying to kill a guy they couldn't kill," Sheppard said. "The death penalty is getting us nothing but broke."Alvord outlasted eight presidents and nine governors. He watched 75 other inmates march to the execution chamber. Of those who have been executed in the last decade, the average length of stay on death row has been about 20 years — half as long as Alvord.Alvord had no close family members, Sheppard said.He did have an ex-wife, Brenda Brock of Michigan.She assumed he had died after her letters to him started coming back unopened in 2003."At least he is released from that cell," Brock said. "I want to say I hope he didn't suffer. But he did suffer. His whole life was suffering."Brock, 62, met Alvord in 1966. She knew he had mental problems, but youth and ignorance made her succumb to his charm, she said. Within a year, they married. While Alvord was jailed on the rape charge, Brock gave birth to a son."What a waste of a life," Brock said. "I'm sure at some point he had some promise and he had something he wanted to be. … If it does any good, I pray for him every day."Times staff writer Mark Puente contributed to this report.