DETECTIVES hunting the killer of Chinese-Australian schoolgirl Karmein Chan are working on 400 new leads drawn from almost 2,000 tip-offs from the public since they released new information about the killer's house last week. But this desperate search for a break-through in the massive manhunt appears to be their last hope of finding the man dubbed Mr Cruel. Taskforce Spectrum, set up to find him 21 months ago after Karmein was abducted from her home at knifepoint, is to be reviewed in May if he has not been found when these new leads are exhausted. Police were swamped with calls within hours of releasing sketch plans and descriptions of the bathroom and bedroom described by two other girls they believe were also abducted by Mr Cruel, but later released. The Taskforce Spectrum head, Detective Inspector David Sprague, has revealed that one of the girls - either Sharon Wills, 10, abducted in December 1988 and held for 18 hours, or Nicola Lynas, 14, snatched in July 1990 and held for 50 hours - peeped undera blindfold to acquire the information, despite being warned not to. ''She was putting herself in extreme danger,'' he said. He has also revealed Mr Cruel told one of the girls his own safety was more important than her life. Det Insp Sprague admits some police opposed revealing the details about where the girls were held, for fear of the girls' safety and of letting Mr Cruel know how much the police knew. ''The release of information may trigger something useful or it could cloud the thinking of a potential witness. ''We are also very conscious that whatever we release, he (Mr Cruel) will be reading, watching and listening too,'' he said. But a Brisbane criminologist, Professor Pal Wilson of Queensland University of Technology, has criticised the police for keeping the house details secret for so long. ''If they feared that, they could have provided protection for the girls,'' he said. He said the chance of new information in the media leading to Mr Cruel decreased as time passed and the crime became stale in people's minds. His criticism drew an angry reply from Victoria's new Police Commissioner, Neil Comrie, who attacked ''academics spouting off the top of their heads''. He said the case detectives were best equipped to make such tactical decisions and they should not be second-guessed. But it is not the first time the task force has been criticised. A shot of Karmein provided by her mother Phyllis Chan, after the abduction on April 13, 1991, was revealed in August that year to be five years old and show her with long hair instead of the short bob she had when abducted. Police said they used the shot because Mrs Chan said it was the most recent available, but she later provided another, taken 18 months before the abduction. Karmein's body was found on vacant land almost a year after her abduction. She had been shot three times. Her parents, John and Phyllis Chan, who emigrated here from Hongkong 11 years ago, then tried to sell their luxury suburban home and the Chinese restaurant where they were working when Karmein was abducted. Mr Chan says they want to return to Hongkong or make a new life in the United States. But the depressed property market here has foiled their plans and he now says they will stay until a buyer can be found. The hunt for Mr Cruel is the Victoria Police's biggest ever investigation. It has cost A$2.7 million and police have compiled more than 8,100 information reports, interviewed more than 15,000 people and driven more than 600,000 kilometres. Task force detectives have travelled interstate to check for similarities any time an abduction was reported. Their investigations have included checking the interior of 3,000 houses in the 15 suburbs under the airport flight path they have pinpointed because both Sharon and Nicola heard planes passing overhead. Their descriptions of loudness and frequency were used by the Civil Aviation Authority to identify flight paths, revealing they related to Tullamarine International Airport in Melbourne's north-west. The details released last week described rooms police fear may have been changed as a result of publicity, so they are asking people to think back to 1988 to 1990. They described an unusual bathroom, with a wash basin close to the shower door, and a bedroom decorated in peach, orange and lemon. It was recreated for a local newspaper by a film production house. Although they don't know enough to release an identikit, police have some physical details of Mr Cruel - sandy hair and eyebrows, 175 cms tall, slim to medium build, aged 30 to 50. And they have a psychological profile of him which portrays him as an apparently intelligent, well-read, well-organised person who may seem nice and be a good neighbour. But they believe someone must have their suspicions and followed up their first press conference last week with another, urging ''the right person'' to come forward. ''That could be a mother, a sister, a wife or a girlfriend. I am sure it would be difficult to come to terms with the fact that someone you know and love has done something like this,'' Det Insp Sprague said. He is urging all Victorians to play ''armchair detective'', to catch the man police believe is a serial criminal who will continue to abduct and perhaps kill young girls. One of the biggest difficulties police face in finding Mr Cruel is that, so far, no one has seen him - except, perhaps, Karmein Chan. Although they say releasing this new batch of information is not an act of desperation, not even the A$300,000 reward has brought police closer to finding him. If this new move and the 2,000 tip-offs don't do so, it seems likely the Spectrum Taskforce will be, if not wound up, at least wound down, and the next we hear of Mr Cruel will be when he strikes again.