TOLEDO, Ohio -- A fellow inmate is suspected of fatally beating a serial killer dubbed the “Angel of Death” inside the cell where he was serving multiple life sentences, authorities said Friday.

No charges have been filed yet and the name of the suspect hasn’t been released, said Lt. Robert Sellers, a State Highway Patrol spokesman. Details about the attack won’t be released until investigators take the case to a grand jury, Sellers said.

Donald Harvey, 64, died Thursday, two days after he was attacked and beaten in his prison cell. Harvey wasn’t alert when he was found Tuesday at the state prison in Toledo, officials said.

Convicted killer Donald Harvey, center, is led back to jail by Laurel County, Ky., Sheriff Floyd Brummett, left, and an unidentified deputy after pleading guilty to eight murder charges and one voluntary manslaughter charge in London, Ky., on Nov. 2, 1987. AP Photo/Ed Reinke

Harvey claimed responsibility for killing more than 50 people during the 1970s and ‘80s. He pleaded guilty in 1987 to killing 37 people, mostly while he worked as a nurse’s aide at hospitals in Cincinnati and London, Kentucky. He later said he was responsible for killing 18 others while working at the Veterans Administration Medical Center in Cincinnati.

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How many people Harvey killed will never be known. He first told his attorney after his arrest that he could only offer an estimate. He then pleaded guilty to avoid the death penalty.

Many were chronically ill patients and he claimed he was trying to end their suffering.

Serial killer Donald Harvey stands before a judge during sentencing in Cincinnati in September 1987. AP Photo/Al Berhman

Harvey used arsenic and cyanide to poison most of his victims, often putting it in the hospital food he served them, prosecutors said. Some patients were suffocated when he let their oxygen tanks run out.

His crimes began in the early 1970s when he was a teen working at Marymount Hospital in Kentucky.

Twenty-one of the people Harvey killed were at the former Drake Memorial Hospital in Cincinnati, where he worked from 1986 to 1987. He was caught after a medical examiner smelled cyanide while performing an autopsy on a victim.