A former nurse's aide convicted of killing more three dozen people died on Thursday, two days after he was attacked and beaten in his Ohio prison cell.

As Ohio Public Radio's Karen Kasler reports, "64-year-old Donald Harvey had been nicknamed the 'Angel of Death' in 1987, after admitting to killing 37 elderly or chronically ill people in hospitals in Cincinnati and rural Kentucky beginning in 1970. But after his conviction, he claimed that he had killed up to 50 people."

Harvey was serving consecutive life sentences. He had been in prison for 30 years when he was assaulted Tuesday inside his cell at the Toledo Correctional Institution, as the Toledo Blade reports:

"He died Thursday at Mercy Health St. Vincent Medical Center. ... The Ohio Highway Patrol continues to investigate his death, said spokesman Lt. Robert Sellers. He would not comment on the attack or Harvey's injuries. Authorities have identified a suspect, but not yet filed charges, Lieutenant Sellers said."

Before Harvey was caught, his hospital co-workers would joke about how many patients died under his care, according to The New York Times. The newspaper adds:

"Mr. Harvey joined in the joking, and because his victims were old or in poor health, their deaths did not arouse much suspicion."He'd say, 'I got another one today,' " the prosecutor told the court. "And everybody thought it was just a joke."

Harvey killed his victims by putting poisons such as cyanide or arsenic in their food, not refilling their oxygen tanks, or suffocating them with pillows. He was finally caught in Cincinnati when he fatally poisoned a man hospitalized after a motorcycle accident. During the motorcyclist's autopsy, the doctor smelled cyanide in the man's stomach cavity, according to the Times.

Harvey pleaded guilty to murders in Ohio and Kentucky, avoiding the death penalty. A former prosecutor in the Kentucky case described Harvey as a cruel man without sympathy for his victims.

"My reaction is he went by the same method by which he killed scores of other people while they were helplessly lying in bed," Tom Handy told the Blade. "I don't want to come off as cold-hearted, but at the same time, I think justice has been rendered."

Harvey has said he would have kept killing had he not been caught. "I felt what I was doing was right," he said. "I was putting people out of their misery. I hope if I'm ever sick and full of tubes or on a respirator someone will come and end it."

But former Hamilton County Prosecutor Arthur Ney Jr., who prosecuted the cases in Cincinnati, disputes the idea that Harvey was a mercy killer.

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