Mr Cruel tormented Melbourne for a decade. 31 years on, we still don't know who he is.

On Sunday night, Australian True Crime Stories will look into the baffling and brutal Australian serial rapist and killer known as Mr Cruel. Here’s what we know about Mr Cruel’s Melbourne terror reign and his helpless victims.

Thirteen-year-old Karmein Chan was babysitting her two younger sisters at their family home in the Melbourne suburb of Templestowe in 1991, when she became the victim of Australia’s most prolific serial rapist Mr Cruel.

And soon-to-be murderer.

It was the school holidays. While their parents were working at the family’s Chinese restaurant 10 minutes from their suburban home, Karmein and her sisters were watching a Marilyn Monroe documentary when they got up to get something from the kitchen at around 9pm.

There, they found a masked man wielding a large knife, his face completely covered by a black balaclava with white stitching around the eyes and mouth. After forcing Karmein’s sisters into a cupboard and barricading them in by pushing a bed up against the door, the man later known as Mr Cruel dragged the teenager through the house, past the family’s Toyota Camry, through the garden gate and out onto the street.

Vice reports Karmein's scent led police to a vacant block 300 metres away. There, the trail went cold, and Karmein wasn't seen or heard from again. A year later, her remains were found in bushland - she'd been shot three times in the head.

Karmein was the fourth of Mr Cruel's official victims - Victorian police linked the perpetrator to three other unsolved violent abductions and sexual assaults. Sadly, Karmein was the only victim, that we know of, who never made it home.

On Sunday night, a new documentary from Australian True Crime Stories into how Mr Cruel terrorised Melbourne for a decade will air on Channel Nine. Here's what we know about Australia's most prolific serial rapist, and murderer, who may still walk the streets today.

Who is Mr Cruel?

Mr Cruel is Australia's most prolific serial rapist, kidnapping and sexually assaulting up to 12 children between the decade of 1985 and 1995.

31 years on from the masked assailant who targeted young girls in the northeastern suburbs of Melbourne, police have never caught the man nicknamed Mr Cruel by local newspapers.

Although authorities suspect the unknown criminal is responsible for a dozen heinous crimes against children, Mr Cruel has only been officially linked to four cases.

As far as we know, Mr Cruel could still be out there, if he is still alive in 2019.

You can watch the trailer for the Mr Cruel investigation on Australian True Crime Stories below. Post continues after video.

Mr Cruel's victims.

Because Mr Cruel has never been caught, there's no way to know how many have been victimised by the perpetrator whose face we've never seen, always covered by a black balaclava.

However, the ABC reports Victorian police have linked Mr Cruel to four cases of kidnapping and sexual assault, one of which resulted in the brutal murder of 13-year-old Karmein Chan.

1. Unidentified victim: Lower Plenty, VIC, August 22, 1987.

On August 22, 1987, Mr Cruel removed a pane of glass from a lounge room window in a house in Melbourne’s Lower Plenty around 4am.

Creeping into the master bedroom, he forced the parents of two children onto their stomachs and tied their hands and feet together, the ABC reports. He locked the adults in a wardrobe, tied their seven-year-old son to his bed, and raped their 11-year-old daughter. He left the house after chopping the phone lines.

2. Sharon Wills: Ringwood, VIC, December 27, 1988.

Just days after Christmas in 1988, the same offender broke into a Ringwood home.

Mr Cruel tied up the adults once more, disabling their phones and demanding money, before kidnapping 10-year-old Sharon Wills - he placed tape over her eyes and put a ball in her mouth to keep her quiet. He assaulted the girl and released her, dressed in rubbish bags, at a high school 18 hours later.

3. Nicola Lynas: Canterbury, VIC, July 3, 1990.

Armed with a knife and a gun, Mr Cruel he broke into a house in Canterbury through a window and tied and gagged 13-year-old Nicola Lynas. According to the victim, Mr Cruel had been watching Nicola walking home from school before abducting her.

Like he did with Sharon, he taped over her eyes before driving her to another house where he assaulted her over 50 hours. Nicola was released in a public area in Kew.

4. Karmein Chan: Templestowe, VIC, April 13, 1991.

Karmein Chan was at home with her two younger sisters when Mr Cruel abducted her from their Templestowe home. He is believed to have cut through a fly screen to open a window.

Although the offender left Karmein's sisters unharmed, tied up and shoved in a wardrobe during the kidnapping, the 13-year-old's body was found a year after her abduction in bushland by a dog walker. Karmein had been shot three times in the head.

Mr Cruel case and why police have never found the killer.

Despite the killer's prolific nature and the violence inflicted on his victims, Mr Cruel has never been caught or identified by police.

The ABC reports hundreds of police have been involved in the case since the 80s. The original investigation Operation Spectrum cost $4 million - police interviewed 27,000 people, searched around 30,000 properties and arrested more than 70 people, mostly related to sex offences.

But still, no Mr Cruel.

What we do know about Mr Cruel from the police investigation, a psychological profile constructed by the Federal Bureau of Investigation (FBI) and the information provided by his living victims includes:

• Mr Cruel was a man aged between 35 and his late 40s at the time of the crimes, slightly built, with sandy or ginger-coloured hair, clean shaven, softly spoken and, according to police, 'quite caring in his own monstrous way'.
• Because Mr Cruel targeted young girls during school holidays, Mr Cruel was believed to be involved with the school system, either as an employee or connected to a school in some other capacity.
• Mr Cruel enjoyed spending lots of time with his victims, which the FBI credited to being an act of dedication - they speculated Mr Cruel may have won awards or been praised for his dedication to his students in his employment.
• Mr Cruel was believed to be operating out of a base near Melbourne's Tullamarine airport - because of the close proximity of all four confirmed crimes, the FBI believed Mr Cruel likely lived and/or worked in the area.
• To his friends, family and neighbours, Mr Cruel would've appeared to be a normal, functioning human being - regarded as kind, quiet and community-minded.

Some of these suspected personality traits made it difficult for police to identify Mr Cruel, along with the precautions he took during and after his crimes.

Mr Cruel also forced his victims to wash and his DNA was never recovered. He also always protected his identity by wearing a mask - police believe Karmein Chan may have seen Mr Cruel's face or recognised him, resulting in her death.

Mr Cruel theories.

There have been many theories surrounding Mr Cruel and his ability to evade police for decades.

One such theory, outlined in an investigation by The Australian, proposes Mr Cruel and the Golden State Killer, a prolific American serial killer, are the same person.

Neither man was ever caught and the similarities between them are uncanny.

Is Mr Cruel the Golden State Killer?

In the early 1980s, California was terrorised by the Golden State Killer.

Much like Mr Cruel, the Golden State Killer was a serial offender who liked to rape young women and girls before murdering them. Both offenders shared remarkable similarities in their style of attack, and their horrific penchant for violent, sexually-based crimes.

The Golden State Killer in California didn't only target young girls and his victims ranged in age from 13 to 41, The Australian reports.

First, he targeted young women and their children. Then, as he grew in confidence, he began targeting couples as they slept in their own homes. According to the FBI, the same man is thought to be responsible for 12 murders, 45 rapes, and 125 burglaries between 1976 and 1986 - when he mysteriously disappeared.

According to The Australian, US authorities confirmed they looked at the possibility that the Golden State Killer might have fled to Australia after he stopped operating suddenly, without explanation, in 1986.

Both men reportedly took breaks during their assaults to eat meals. Both used knives and guns as a means to subdue, and then kill, their victims. Both engaged in pretend conversations with others during their crimes. Both used expert knots to keep their victims tied up, and they told the women and girls they raped they were "only there to rob them".

Australian police, however, said they investigated the potential link to Mr Cruel, but ruled out the possibility that the crimes were committed by the same man.

In 2018, police tracked down a man named Joseph James DeAngelo through genetic genealogy. He was identified as the Golden State Killer and charged with his crimes.

Obsessed with true crime? Listen to Mia Freedman's fascinating interview with The Teacher's Pet podcast creator and journalist Hedley Thomas below. Post continues after audio.

Mr Cruel Australian true crime documentary.

Almost 32 years after Mr Cruel kidnapped and raped his first victim, that we know of, he remains at large.

If he was alive today, the ABC reports he would be in his 60s, and likely still living in Melbourne's northeastern suburbs.

On Sunday April 14, a documentary will re-examine Mr Cruel's crimes in the late 80s and early 90s as part of Channel Nine‘s Australian Crime Stories series.

The Mr Cruel episode is set to air on Sunday night at 9pm on Nine and also on the network’s on-demand streaming service 9Now.

Will you be watching the documentary on Mr Cruel? Why do you think police have never been able to identify the serial rapist and murderer?