NEWARK, N.J. (AP) _ Death has been Charles Cullen's constant companion nearly all his life.

The nurse who claims to have killed 30 and 40 seriously ill patients at hospitals in New Jersey and Pennsylvania tried at least once to take his own life by lighting a charcoal fire in his bathtub, police say.

His parents died when he was young, as did two siblings. Over a 16-year career at nine hospitals and a nursing home, he watched the old and sick die. He also cared for a brother who died of cancer.

Cullen, 43, is charged with killing a Roman Catholic Church official and attempting to kill another patient at Somerset Medical Center in Somerville.

Authorities are reviewing patient records and fielding calls from nervous relatives, trying to evaluate Cullen's claims that he administered fatal overdoses of heart medication to seriously ill patients in Pennsylvania and New Jersey to put them out of their misery.

``Mercy killing is a common defense,'' said Dr. Michael Welner, an associate professor of psychiatry at New York University Medical Center and an expert on serial killers. ``But that is a rationalization a person employs to convince themselves they're doing the right thing.''

Death touched Cullen early on. His father died when Cullen was an infant, and his mother when he was in high school. The West Orange family had eight children, two of whom have also died.

Cullen quit high school and joined the Navy in 1978, after his mother died, then returned to study nursing at Mountainside Hospital School of Nursing in Montclair, graduating in 1987.

He married and had two daughters before he and his wife separated around 1992, later divorcing. He also cared for a brother who died of cancer.

On Jan. 3, 2000, Cullen tried to kill himself by bringing a hibachi full of charcoal into the bathtub, sealing up his Phillipsburg, N.J. apartment, and waiting for death, authorities said. A woman who lived above him smelled what she believed was kerosene wafting from Cullen's basement apartment. She went downstairs, knocked several times on the door, but got no answer, and called police.

They arrived a few minutes later, forced open a screen door and banged on the interior door until Cullen opened it. Police smelled the burning charcoal and questioned Cullen about it.

Cullen ``said he lit the fire to keep warm because the heat wasn't working,'' according to a police report. But police also found that the air ducts had been stuffed in an apparent attempt to let carbon monoxide build up in the room.

``It was an obvious suicide attempt,'' Detective Lt. Larry Marino said Wednesday.

Police took him to a crisis center, where a social worker said she remembered helping him after a previous suicide attempt. He walked out of the facility shortly afterward, authorities said.

Three years earlier, in 1997, Cullen was taken to Greystone Park Psychiatric Hospital after being treated for depression in the emergency room of Warren Hospital. There, he argued fiercely with a doctor who wanted to do a blood test on him, a necessary precursor to admission to Greystone, police said.

``He refused, but finally he gave in and allowed the doctor to take the blood,'' Marino said.

Cullen came back to police headquarters about six weeks later, filing a report accusing the doctor of forcing him into giving blood, but no further action was taken, Marino said.

His other brush with Phillipsburg police came in 1994, when Cullen told officers someone was making threatening phone calls to his apartment. He told police he suspected that a relative of his estranged wife was making them, Marino said. No one was ever charged, Marino said.

A few years later, he filed for bankruptcy.

Cullen bounced from job to job in New Jersey and Pennsylvania, sometimes leaving on his own, sometimes being fired. Authorities now say a flawed regulatory system that does not permit the sharing of information on fired health care employees, coupled with a severe nursing shortage, enabled Cullen to move from place to place without new employers knowing he was the subject of a murder investigation.

Welner said that detecting murders in a hospital is extremely difficult.

Nurses ``are aware of which medicine to get, when the shift changes, when they can be alone with a patient,'' he said. Moreover, ``there is no screaming, thrashing victim. There's just a silent poisoning. There's not so much as a whimper. It's as anonymous as a person drifting off to sleep.''

Cullen's neighbors recall an unremarkable man, quiet and somewhat isolated, who got their attention only when his car blocked their driveways or when he failed to shovel the snow from his sidewalk. When they complained, Cullen would get defensive, claiming he was being persecuted by the neighborhood.

Cullen kept his yard neat, and planted a tidy garden. But he left his dog chained outside in bitterly cold weather, and eventually it was taken away by animal welfare officers.