Police have revealed a suspected serial killer believed to be responsible for the murders of three people in South Australia lived close to each of them when they were killed, and is currently living freely in Victoria.

Key points: A secret police taskforce has forensically linked three murders in SA

A secret police taskforce has forensically linked three murders in SA Phyllis Harrison, Beverley Hanley and Stephen Newton were all found dead after suspected robberies

Phyllis Harrison, Beverley Hanley and Stephen Newton were all found dead after suspected robberies Police believe the same person is responsible for each crime

A secret police taskforce found a forensic link between the deaths of grandmothers Phyllis Harrison in 1998 and Beverley Hanley in 2010, and Mount Gambier man Stephen Newton in 2011.

Major Crime officer-in-charge Detective Superintendent Des Bray said the 39-year-old man suspected of killing the trio lived within 10 minutes of each of them at the time each crime was committed.

The suspect now lives in the Sunraysia region of Victoria, and is being treated by police as a danger to the public.

"We've advised local police of the circumstances of these deaths and the potential risk that that person poses," Superintendent Bray told a media conference.

"We clearly know where he is, he knows that he's been a focus of the investigation for many years, he knows that we're looking at it again now.

"We're quite comfortable with him knowing about it now.

"To jump in early and arrest him without sufficient evidence would simply expose the public to more risk."

Sorry, this video has expired Superintendent Des Bray discusses the suspect

Police have been reviewing the three murder cases since January.

They said forensic evidence including DNA and new information coming to hand had left investigators confident the same suspect was involved in all three deaths.

"Each attack was extremely brutal," Superintendent Bray said.

"I would encourage anybody with information to think about it, consider their conscience, consider the families of each of the victims and do the right thing now and come forward.

"It is clear that some people have withheld information and some people have told lies, and some of those people may be scared of this offender."

Theft linked to all three killings

Superintendent Bray said there was proof theft was the motive in all three deaths.

"He was known to all three victims and at the time of the deaths lived within about 10 minutes of them," he said.

Ms Harrison, 71, was found dead in her Elizabeth South home in 1998 with multiple stab wounds.

Phyllis Harrison was found dead in her ransacked home. ( SA Police )

Her house on Harvey Road was ransacked, but it was unclear what was stolen.

Ms Hanley, 64, was killed in her Elizabeth North home in 2010. She suffered severe head injuries, her house was ransacked and her handbag was stolen.

Her son previously said she was hit with a cricket bat at her Homington Road home.

Police have previously linked a bloodied footprint from skate shoes and a telephone cord containing a DNA profile to her death.

"Importantly, a witness heard her between that time talking to a male near the back door of her house, who she apparently knew," Superintendent Bray said.

"During the course of the conversation the voices became elevated and it was clear and argument developed, followed by a scream, some loud thugs of somebody apparently being struck and then silence."

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The third case is the murder of Mr Newton, 55, whose badly decomposed body was found in his unit in 2011.

At the time, police would not reveal how Mr Newton was killed but have now said it was the result of an assault.

A range of items, including a TV, DVDs, a computer game console and games were taken from the home on Davison Street.

Mr Newton's body was found on November 11, but police believe he was killed between September 23 and 29.

In that case, a man was later charged and convicted in relation to property theft and was sentenced to seven months' jail in 2012.

Daughter describes finding mother on the floor

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Police have previously released appeals about the cases, and earlier this year Ms Harrison's daughters spoke to Crime Stoppers about their mother's death.

"My son went in first and then I went in and I noticed that she was laying on the floor and I just freaked out," daughter Diane Smoker said.

The family has previously indicated it believes Ms Harrison's killer was someone she knew.

"They got into the house with her acknowledgment and that's when they took advantage of her," daughter Julie Lane said.

Police have asked anyone with information to contact Crime Stoppers on 1800 333 000.