Karmein Chan was abducted while babysitting. Her body was found a year later and her killer has never been found. Photo / Supplied

What if Australia has been wrong about Mr Cruel all along?

The man who terrorised Victoria in the 1980s with a series of violent, disturbing attacks — often on children — has never been caught. Australians have always assumed he was a local who went underground or died when the attacks stopped in 1991.

But there's another theory that amateur crime buffs think holds weight and that police on the other side of the world were forced to investigate.

Police in Victoria and San Francisco compared notes on the notorious Golden State Killer, who shared a remarkable connection that made some wonder whether he and Mr Cruel were the same person, the Australian reported.

Before Mr Cruel attacked four girls under the age of 13 in Melbourne's outer suburbs between 1987 and 1991, culminating in the unsolved murder of Karmein Chan, the Golden State Killer was doing exactly the same thing on America's west coast.

He murdered 12 people and raped 45 women in a series of depraved attacks during the 1970s and early 1980s. He left blood everywhere but covered his tracks and was never caught.

Then suddenly, in 1986, the attacks stopped and the killer disappeared. A year later, Mr Cruel arrived in Melbourne.

The two lived by the same criminal code. The Australian reports they both took breaks to eat meals, were armed with a knife and a gun, pretended to have conversations with people who weren't there and used expert knots to tie up their victims — and in Mr Cruel's case — to tie up parents while he attacked their children.

The links between the two killers didn't end there.

Both wore dark-coloured balaclavas and had long hair protruding from underneath — and because of that the police sketches are almost identical. Both crept into homes holding large knives and waited to be found. Both would be between 60 and 75 years old if still alive and both were pathologically meticulous.

They also came under the microscope of the Federal Bureau of Investigation, despite the crimes occurring on different sides of the planet.

In 1991, after the disappearance of Karmein Chan, the FBI sent a letter to Victoria Police. It detailed steps they should take to catch Mr Cruel, what his interests were, how his relationships likely played out and why he attacked where and when he did.

The FBI noted that "the offender has an intense interest in children … will have his own home-made pornography [and] would typically live in a single-family residence, one with a garage or carport". The letter, dated April 24, 1991, stated that if the killer was in a relationship, "the partner would be aware of sexual dysfunctions".

It wasn't the last time Mr Cruel's file would land on the desk of law enforcement in the United States.

In 2016, after a renewed appeal for information into the unsolved murders committed by the so-called Golden State Killer, retired Los Angeles Sheriff's Department detective David Gates suggested the GSK closely resembled a man wanted for burglaries in the mid-1980s who police later discovered had moved to Australia. When contacted by The Australian, Gates said "the fair-haired college kid" he had investigated was "just a nasty piece of work".

On the other side of the world, Victoria Police were also watching the serial killer in California, but ruled out any suggestion the two were the same person.

The Golden State Killer's story resurfaced recently thanks to a documentary entitled Unmasking a Killer. The five-part series claims to "take viewers inside the investigation, the case files and the mind of the Golden State Killer — a man believed to be the most prolific uncaught rapist and serial killer in the nation".

The project, 10 years in the making, includes interviews with investigators and survivors.

The Golden State Killer first struck in 1978 with the double murder of Brian and Katie Maggiore in Sacramento. A year later he broke into the home of Robert Offerman and his girlfriend Debra Manning, tied them up and shot them.

Over the next six years he would kill three more couples and two single women. A number of the murders were in Goleta and Irvine, suggesting the killer returned to neighbourhoods he was familiar with.

The FBI suggested Mr Cruel did exactly the same thing. In their letter to Victorian Police, they said they believed the offender "may reside in the vicinity of the first assault".

"This is further strengthened by the fact that the offender has returned to that same general area in the fourth assault," the bureau said.

The fourth assault they referred to followed the abduction and assaults of three young girls. One is described only as "an 11-year-old girl" and the other two were Nicola Lynas and Sharon Wills.

On the fourth occasion, Mr Cruel took Karmein Chan, 13, from her home while she was babysitting her sisters, aged 9 and 7. The teen was confronted with the masked intruder during an television ad break while the three girls were watching a movie in Karmein's bedroom.

Mr Cruel grabbed the two younger girls and forced them into a cupboard before abducting Karmein.

Her body was found nearly a year later at a landfill site in Edgars Creek, not far from the Chan family home.