The "Angel of Death" serial killer, who admitted to killing three dozen hospital patients in Ohio and Kentucky during the 1970s and 80s, has died after being attacked in his prison cell.
A prisons spokeswoman says Donald Harvey, 64, died Thursday at 9.08am (2am Friday NZ time), two days after state troopers say he was found beaten in his cell at the state's prison in Toledo.
The assault happened about 2.20pm on Tuesday (7am Wednesday NZ time), and Lieutenant Robert Sellers told the Toledo Blade that they have a suspect, but did not release anymore information, the Daily Mail reports.
Harvey became known as the "Angel of Death" after pleading guilty in 1987 to 37 murders.
He later said he had killed as many as 50 more.
He committed the murders while working as a hospital aide, using a variety of methods, including turning off ventilators, giving patients fluid infected with hepatitis B, and suffocation.
But many of the killings involved his favourite poisons, arsenic and cyanide, which he would administer in food, using injections, or through an IV.
Harvey had suffered sexual abuse at the hands of his uncle and a neighbour between the ages of 4 and 20, and was raped by his male roommate in 1970, when he was 18.
He also became fascinated by witchcraft and neo-Nazi groups as he grew older.
His first kill was on May 30, 1970 when he killed 88-year-old Logan Evans with a sheet of plastic and a pillow, and listened to his heart with a stethoscope as he died.
The following day he accidentally killed James Tyree, 69, when he used the wrong size catheter on him.
His third victim, on June 22, was also the first of a series of "mercy killings". He said Elizabeth Wyatt, 42, had been praying to die so he turned down her oxygen supply until she died.
He killed people at Marymount Hospital in London, Kentucky, the Cincinnati VA Medical Hospital and Cincinnati's Drake Memorial Hospital.
But his murders weren't restricted to hospitals, a Radford University psychology report said.
When he suspected his lover, Carl Hoeweler, had been cheating on him, he dosed him with arsenic so he would be too ill to leave their apartment.
Hoeweler didn't die, but his father and brother-in-law were less lucky.
Harvey poisoned Carl Hoeweler, 82, with arsenic, and brother-in-law Howard Vetter died after Harvey accidentally served him wood alcohol instead of vodka. Both died in 1983.
Between 1983 and 1985, Harvey also killed neighbours Helen Metzger, 63, and Edward Wilson, 32, with arsenic because he felt they threatened his relationship with Hoeweler.
After being caught, he agreed to a plea deal that allowed him to avoid the death penalty and was instead serving 15 life sentences.
He would have been eligible for parole in 2043 at 91 years old.