Percy's death in July last year, aged 64 and after serving 44 years as a prisoner, was investigated because it is mandatory to do so in Victoria for the deaths of people in custody.

Coroner Paresa Spanos on Wednesday found Percy died from lung cancer on July 24, having first complained of headaches and pain in the pelvis, lower back and legs about six weeks earlier.

Sergeant David Dimsey told the court Percy was one of Australia's most violent criminals who had been in custody since July 1969, when he was arrested for the murder of 12-year-old Yvonne Tuohy.

Percy abducted the girl from a Warneet beach and told police he killed her, but was found not guilty of murder on the grounds of insanity. He was detained at the governor's pleasure and never released.

His detention was reviewed three times by the Supreme Court, but on each occasion it was determined his release would present a danger to the community, Ms Spanos said in her findings.

Percy grew up in NSW and joined the navy when he was 19, and has been linked to the deaths or disappearances of eight other children across Australia.

They are: friends Christine Sharrock and Marianne Schmidt, both 15, who were murdered on a Sydney beach in January 1965; the Beaumont children – Jane, 9, Arnna, 7, and Grant, 4 – who disappeared in Adelaide on Australia Day in 1966; Allen Redston, 6, who was abducted and killed in a Canberra suburb in September 1966; Simon Brook, 3, who was killed in Sydney in May 1968; and Linda Stilwell, 7, who was abducted from St Kilda in August 1968.

No charges in those crimes have ever been laid.

In the days before his death, Percy was visited by Deputy State Coroner Iain West in the secure ward of St Vincent’s Hospital and asked if he was involved in the abduction and murder of Linda Stilwell.

Percy said he had no knowledge about the case and denied he was the killer.