CAMBRIDGE, Mass. -- A man who claims he thought he was killing Nazis when he fatally shot seven co-workers testified Thursday that he left a previous job at a nuclear plant because "I had gone crazy."

"I had an escalating mental illness which eventually led to a suicide attempt," said Michael McDermott, who claimed he was harassed by an ex-girlfriend who worked with him at the Maine Yankee plant. "I cut my wrist open."

McDermott, who has pleaded innocent by reason of insanity in the Dec. 26, 2000, massacre at Edgewater Technology in Wakefield, also claimed he was raped several times by a neighbor when he was 8 years old, though it was never reported to police. He said he father later pushed him to join the military after high school.

Prosecutors have said McDermott planned the slayings in retaliation for the company's plans to withhold his wages to pay $5,600 in back taxes he owed to the IRS.

His attorney, however, said the 43-year-old software engineer is so insane that he believes he killed Adolf Hitler and six Nazi generals.

McDermott testified Thursday that he believes he died in 1940 and that he hears voices telling him what to do.

"The voices in my head, I clustered them into different groups," he said. "The major one I call the chorus. Its job is to tell me what a bad person I am. ...The chorus continuously tells me what a bad person I am, what a waste of space and skin and air I am."

One of the "non-chorus" groups, he said, tells him to steal things. He said he stole boxes of laboratory glassware while working for Duracell, but had no use for them.

McDermott claimed he was exposed to radiation while working at the plant, which "pretty much killed my thyroid."

McDermott said he got a vasectomy after his 1992 marriage, because: "Neither my wife nor I wanted children and I had bad genes. I wouldn't want to pass my craziness to someone else and I had years of exposure to radiation."

McDermott also believes St. Michael appeared to him before the shootings and told him he didn't have a soul but could earn one if he prevented the Holocaust, defense attorney Kevin Reddington told jurors Wednesday.