Ailing Victorian child killer Derek Percy will be questioned until the day he dies as police pursue confessions about unsolved crimes.
The family of seven-year-old Linda Stilwell wants the dying killer to be made to give evidence from his hospital bed over her 1968 disappearance in Melbourne.
Percy is also a suspect in NSW, Canberra and Adelaide for long-standing unsolved murders and disappearances and Victorian police will continue to quiz him over those matters.
"Victoria Police have been doing that and will continue to do that until he dies," said NSW Detective Chief Inspector John Lehmann from the unsolved homicide team.
Percy's DNA was made available to NSW police during the past year but there have been no breakthroughs in the cold case murders of two teenagers and a three-year-old boy in which Percy is a suspect.
"There's no developments in those cases as a result of us receiving Percy's DNA at this stage," Det Chief Insp Lehmann told AAP.
Last year it was revealed a blood stain taken from the scene of the 1965 murders of teenagers Christine Sharrock and Marianne Schmidt on Sydney's Wanda Beach could provide a breakthrough in the case, in which Percy is a suspect.
But DNA testing is not advanced enough to make a definitive link, because the evidence is so old.
Scientists say there is still a lot of work to do before the sample can be used to match suspects' DNA.
"We're a long way off," Det Chief Insp Lehmann said.
"That blood or possible blood is still being examined to try and have it enhanced to positively identify DNA."
Percy, 64, has cancer and is in a secure Melbourne hospital ward.
The Victorian coroner is looking at whether Percy can give evidence from his bedside over Linda Stilwell's disappearance, but her family's lawyers are yet to make a formal application.
The coroner is making further inquiries about the intended application and Percy's medical state to work out how Linda's coronial investigation will proceed.
Percy is also a suspect in the unsolved murders of six-year-old Alan Redston in Canberra in 1966, three-year-old Simon Brook in Sydney in 1968, and the disappearance of the three Beaumont children in Adelaide in 1966.
