Ashley Mervyn Coulston will forever be one of Australia's most notorious killers.
He was sentenced to life in prison in 1992 for the brutal murders of three people in a home in Burwood, Victoria, after posing as a potential new tenant.
However, police say he believes he may be responsible for a series of rapes in Queensland and New South Wales in the late 1970s and 1980s.
Ashley Mervyn Coulston (pictured) will forever be one of Australia's most notorious killers
Detectives claim that Coulston went under the radar for decades before he brutally murdered two student teachers at Burwood on July 26, 1992, after visiting his girlfriend in the hospital.
Anne Smerdon and Kerryn Henstridge were killed after Coulston responded to his newspaper ad about a new roommate, according to court documents.
Anne's brother-in-law, Peter Dempsey, 27, was also in the house when Coulston broke in and tied the three in cream ties. He covered his head before shooting them in an execution-style killing.
Coulston was arrested five weeks later, on September 1, when he attacked a couple on St Kilda Road, in Melbourne, and threatened them at gunpoint.
The then 36-year-old walked the couple, Richard and Anne Shalagin, to a dark area of the Botanical Gardens before tethering Anne.
Richard attacked Coulston immediately, giving Anne enough time to run for help.
"I knew that if he did not do something, we were dead," Shalagin told Sunday Night.
Coulston had seen and responded to an ad in an Anne Smerdon newspaper (right) and Kerryn Henstridge (left) of a new roommate in his Burwood home
Anne soon arrested two security agents, who called the police.
Coulston was arrested and quickly told the officers he was trying to rob the Shalagins because he was depressed because he was unemployed.
The detectives said they found their claims hard to believe when they discovered their "kit," which included a knife, handcuffs, balaclava, gloves, a clipped rifle, bullets and cable ties.
Officers soon began to relate similarities between Coulston's attack on the couple and the Burwood murders.
Anne's brother-in-law, Peter Dempsey (pictured), was also in the house when Coulston broke through and tied the three of them in cream wool ties. He put a towel or a robe over each of their heads before shooting each one in the head once
Detective Mick Stefanovic said he began investigating the possibility of more crimes committed by Coulston.
It did not take long to find one.
At the age of 14, Coulston kidnapped two primary school teachers at gunpoint in Tamgambalanga, Victoria, before forcing the couple to go to Sydney.
However, the two women were able to get help in New South Wales after alerting an employee at the service station.
Coulston was sentenced to three months in a juvenile facility.
When he was released, his family moved to Kyogle, in northern New South Wales.
Six years later, an assailant with a balaclava committed a series of rapes in the Gold Coast and Tweed Heads.
The rapist often attacked the couples, tying the man before sexually attacking the woman.
The attacks, which occurred between February 1979 and 1980, ended after the death of Jeffrey Parkinson, who was shot five times after he tried to prevent the rapist from attacking his date.
However, police say he believes he may be responsible for a series of rapes in Queensland and New South Wales during the late 1970s and 1980s (in the picture: Coulston off the court)
In the late 1980s, Coulston moved to Sydney and began living with Cathy Walker and her husband in Sydney.
Five years later, a serial rapist emerged in southern Sydney, with five attacks in just two years.
Robin Napper, a crime forensic expert and DNA expert, said Coulston is suspected of the rapes in Gold Coast and Sydney, as well as the murder of Parkinson's.
Robin Napper (pictured), a crime forensic expert and DNA expert, said Coulston is suspected of rapes in the Gold Coast and Sydney, as well as Parkinson's murder.
Although Coulston DNA was taken in 2000, Napper said it is unlikely that he has been tested against these crimes.
"Coulston is a red-hot suspect for rapes with ski masks in Queensland and for the murder of Parkinson and the Sutherland rapes." When he was caught in Victoria in 1992, you can analyze his timeline, his behavioral instincts, everything about him, and DNA is the last piece of the puzzle.
"If you do, then you can confirm once and for all that he's probably one of the most dangerous serial killers that Australia has ever had."