Mr Cruel is the moniker for an unidentified Australian serial child rapist who attacked three girls in the northern and eastern suburbs of Melbourne in the late 1980s and early 1990s.

Mr Cruel has never been identified, and his three confirmed attacks and the suspected murder remain unsolved cold cases.

In April 2016, twenty-five years after the death of Chan, Victoria Police increased the reward for information that leads to the perpetrator's arrest and conviction, from A$100,000 to A$1,000,000.

On 22 August 1987 in Lower Plenty, a man wearing a balaclava broke into a family home at 4:00 am, armed with a knife and a handgun.

[12] Mr Cruel meticulously planned his crimes; for example, in one case, he abducted a girl and told her he would release her in exactly fifty hours, which he did.

The same two victims told detectives that they had heard planes landing, leading police to believe the house was on one of the flight paths to Melbourne Airport.

[15][17] The head of the Spectrum Task Force, David Sprague, said that some exhibits had not ever been examined by forensics, and had either been lost or thrown out.

[15] The police established a Rape Squad in April 1989, with nine detectives dedicated to investigating serial rapists throughout Victoria, particularly in Melbourne.

[18][19] On 14 December 2010, police announced that the Apollo Task Force had been established about eight months earlier, following substantial new intelligence.

[11] Earlier in 2013, the Herald Sun reported that convicted serial child rapist Robert Keith Knight, who committed suicide in 2013, had been a person of interest.

[22] On 9 April 2016, the Herald Sun newspaper published details of the Spectrum Task Force's dossiers on seven suspects, known as the Sierra Files, that were produced with the assistance of the US FBI.

Detectives had been issued with an instruction in 1994 following the disbandment of the Spectrum Task Force that if another child was abducted, then all the Sierra Files suspects were to be arrested and questioned.

[10] In a 2019 television documentary, retired Detective Chris O'Connor said that there was "broadly speaking perhaps up to a dozen" victims for the investigation.