William Macdonald murdered and mutilated four men with a hunting knife, taking one victim's genitals home in a paper bag before throwing them off the Harbour Bridge.

The gruesome slayings earned him the nickname "The Mutilator" and a life sentence in prison.

"My life has improved since I came to jail," he told a Fairfax journalist in 1995. ""It is terrible out there; people aren't even safe in their own homes."

Macdonald was regarded as Australia's first serial killer. He attacked his victims in The Domain, Moore Park, Darlinghurst and Concord. When he was stalking his victims, in 1961 and 1962, the city's homeless fought to find shelter in hostels and refuges.

He was eventually arrested through the first successful use of a police Identikit sketch. By the time he died last year, aged 90, he was the longest-serving inmate in NSW.

Macdonald, a vegetarian who loved classical music, had no desire to leave jail, saying he "wouldn't last five minutes" on the outside. He spent 52 years behind bars.

Inquests are held into all deaths in custody. On Thursday, Deputy State Coroner Teresa O'Sullivan delivered her findings into Macdonald's death, finding he died of complications arising from a gastronintestinal obstruction. "Mr Macdonald's death is not suspicious and he died of natural causes," she said.

On May 11 last year, Macdonald complained of severe abdominal pain. He was transferred from Long Bay jail to a secure annex of the Prince of Wales Hospital, but died the next day.

Born in England, Macdonald had been diagnosed with schizophrenia as a teen. He was conscripted into the British Army, where he was raped by an officer. He confessed to the four Sydney killings and to strangling a man in Brisbane, saying voices convinced him his victims were "the corporal" who had attacked him.

Explaining why he stabbed and castrated Albert Greenfield in The Domain, Macdonald told police: "I thought when the corporal attacked me he took my life away. So I thought I'd destroy his sex the same way."

It also emerged that one intended victim had a lucky escape after meeting the murderer in Redfern.

"I said, 'Would you like to come for a drink?'" Macdonald recalled. "He said, 'All right but you've got to be careful where you go these days ... Maybe The Mutilator is there ... He could be drinking in this hotel'."

Macdonald was standing over the sleeping man with a sabre when the compulsion to kill left him and he went back to bed.

Despite three psychiatrists testifying at his trial that he was mentally ill, Macdonald was convicted of murder and jailed for life.

A prison warder once took him to Cessnock, where he bought a mandolin from a music shop and was driven around the vineyards. But in an interview with Fairfax in 1995, Macdonald said "the idea of staying out there frightens me". He feared he would kill again.

"I wouldn't want a new start; I would be afraid that I would do the same thing again," he said. "They say a leopard never changes his spots. There is something in me and it's in-built; it is something I can't change."