Derek Ernest Percy, a suspect in the September 1966 murder of Canberra boy Allen Redston is in palliative care at the secure ward of St Vincent's Hospital and has been told he will not survive.

Linked to the deaths and disappearance of nine children in Victoria, NSW, South Australia and the ACT, Percy was interviewed by police in Melbourne in 2005 over the death of Redston.

The interview shed little light on the death of the blond-haired six-year-old, and authorities consistently said the case remained open to review should new evidence come forward. Police were told on Tuesday that Percy was unlikely to live more than two weeks.

Redston, a pupil at the then South Curtin Primary School, disappeared from outside a friend's house in Holman Street, Curtin, sparking a huge police search.

His body was discovered the next day among long reeds in the Yarralumla Creek bed.

With hands and feet bound, the boy was wrapped in a green floral dressing gown and several pieces of carpet and had rope looped around his neck. He was badly beaten and had died from strangulation.

Detectives regularly visited 64-year-old Percy after he was diagnosed in the hope he would make a deathbed confession. But while not denying any of the crimes he has not implicated himself. ''He just says it might have been him, he just doesn't remember,'' an investigator said.

It has been Percy's consistent line since he was first arrested 44 years ago as a young naval rating.

Detectives are expected to approach the frail inmate again.

Percy has tried to avoid giving evidence at the inquest into the case of Linda Stilwell, who was last seen playing on the St Kilda foreshore in Melbourne on August 10, 1968. He has been in custody since his arrest hours after the murder of Yvonne Elizabeth Tuohy, 12, who was abducted from the beach at Warneet, Victoria, on July 27, 1969. Percy was found not guilty on the grounds of insanity and remains in custody.

In 2004, then Senior Detective Wayne Newman was instructed to prepare a Coroner's brief for an inquest into the death of Stilwell. What he uncovered linked Percy to a series of unsolved murders and abductions.

It started a two-year operation that named Percy as a suspect in the murders of Redston; Christine Sharrock and Marianne Schmidt on Sydney's Wanda Beach in 1965; the Beaumont children (Jane, 9, Arnna, 7, and Grant, 4) abducted in Adelaide, in 1966; Simon Brook, 3, killed in Sydney in 1968; and Stilwell.

When Percy was arrested, police found maps, one with a line drawn past the spot where Stilwell was last seen. A woman told police she saw her at St Kilda the day she disappeared near a man wearing a dark spray jacket. When Percy was arrested for the Tuohy murder, he was photographed wearing the same style of jacket.

In 2007, police found boxes filled with material from Percy in a storage depot. It included clippings on sex crimes, stories on child abductions and items that appeared to implicate him in unsolved murders.

In 2011, ACT Attorney-General Simon Corbell said he would consider requests from investigators studying any unsolved murders.