Victoria Police announced on Tuesday that new suspects had emerged this year and a fresh covert task force codenamed Apollo was established eight months ago to track down the Melbourne child killer, pedophile and rapist.
Mr Cruel struck fear into the hearts of families in Melbourne's suburbs and was believed to be responsible for at least four child kidnappings and sexual assaults from 1988 to 1991, including the murder of Karmein Chan in 1991.
Karmein, 13, was kidnapped from her home while babysitting her sisters on April 13, 1991. Her body was found with shotgun wounds to the head in Thomastown a year later.
Mr Cruel may have been a monster but did not necessarily look like one, police believe.
"There are members in our society that hold a key for us solving this investigation and certainly we would hope that they would come forward and provide that information," Superintendent Doug Fryer told reporters.
Detectives built a profile of a man aged between 35 and late 40s, slightly built, with sandy or ginger-coloured hair, clean shaven, softly spoken and "quite caring in his own monstrous way".
"The person who committed these crimes is in amongst our society or was at the time of them; he was associating with people and more than likely held a job down.
"So, there is someone out there who has got information we think that hasn't passed on as yet; there is also a $300,000 reward to assist in solving these horrific crimes.
"I don't think Victoria is ever going to forget this series of crimes; they were that horrendous."
Children who are believed to have all been victims of Mr Cruel told police he used terms such as "bozo", "worry wart" and "missy" before releasing them.
Victims reported hearing planes overhead during their abductions, which was matched up with flight paths around the suburb of Pascoe Vale and neighbouring areas in Melbourne's north.
Retired detective Colin McLaren, who led the original Spectrum task force investigation into Mr Cruel, said the case was the one that still lingered two decades later.
"He was very much like a man in the street, that was the most difficult thing about it," Mr McLaren said.
"We weren't looking for someone who was six foot six or someone who perhaps had a peculiar smell about him.
"He was just very normal.
"I probably don't know of any other more important case that I've worked on that still is unsolved."
About 15,000 people were interviewed as part of the first investigation.
Supt Fryer said more than 12,000 separate pieces of information had been reviewed and cross-referenced with new details as part of the investigation.
Police have not ruled out the possibility Mr Cruel had since fled the country, died or committed suicide.