Politicians have said the details of the decision to release of London cabbie rapist John Worboys should be published and properly scrutinised before he is set free from jail.
The head of a parliamentary committee called for the Parole Board to reveal its reasons for deciding to release the prolific sex attacker, who has served his minimum sentence.
Yvette Cooper, chairwoman of the Home Affairs Select Committee, said she was "really shocked" by the announcement on Thursday and called for more transparency.
Her comments came as Jean Clayton, the taxi driver's ex-wife, spoke out to say he should "never be let out".
Worboys, a former stripper and adult film star, was jailed indefinitely in 2009, with a minimum term of eight years, for drugging and sexually assaulting women passengers.
He was convicted of attacking 12 victims but it is feared he may have assaulted more than 100. At the time of his sentencing many believed the jail time to be too short.
The Parole Board's decision sparked an outcry from charities and support groups when it was made public, with campaigners labelling the 60-year-old’s jail time "woefully short" ".
Ms Clayton, 60, who was married to Worboys between 1991 and 1995, told the Sun that the decision was wrong and said she believed his "next step would have been murder" had he not been caught.
"I feel utter disgust. If he hadn't been caught and taken to court he would have murdered somebody. It's very scary," she said.
The mother-of-three said she ended their relationship after she caught him spying on her two daughters when they were teenagers.
Lawyer Harriet Wistrich said two victims had not been informed of the decision to release Worboys.
She told Channel 4 News the first they learned of the planned release was while "listening on the radio, cooking tea for the kids".
She said: "They've both said they're absolutely sick and disgusted and shocked to the core about it."
It is understood all those who were signed up to a victim contact scheme were informed as soon as the parole board decision was made.
However Labour MP Stella Creasy called on Justice Secretary David Lidington to investigate the alleged failure to notify victims.
She wrote on twitter: "If true that no notice of parole hearing given to the 100 victims then no chance to have their voices heard = no justice. Hope @DLidington will investigate if this is the case and show £VAWG (violence against women and girls) a priority across Government."
Chairman of the Parole Board Professor Nick Hardwick has said he is "very concerned" that the victims of serial rapist John Worboys were not told of his imminent release and added that this must have been "very distressing" for them.
Worboys, became known as the "black cab rapist" after being found guilty of 19 charges of drugging and sexually assaulting 12 passengers, and in one case raping a woman.
But police said in 2010 that his alleged victims numbered 102 after more people came forward following his trial and conviction.
Many of victims were young women who had been drinking in the West End and Chelsea. He offered them Champagne spiked with powerful sedatives which left the women unable to protect themselves as he pounced on them in the back of the vehicle.
At his sentencing Worboys was told he would not be released until parole officials were convinced he did not pose a threat to women.
Ms Cooper said his crimes were "the most appalling and vile" and there were "serious questions" over the Parole Board's decision.
"Given the seriousness of this case, the Parole Board should publish their reasons immediately so both the decision and the process can be scrutinised before this man is released,” she said.
"We also need to know what information and support was given to all the victims before this decision was taken."
Her intervention raises the prospect that senior members of the Parole Board could be hauled before MPs for a grilling over the decision.
In a statement on Thursday the Parole Board - which is independent of, but sponsored by, the Ministry of Justice - said: "We can confirm that a three member panel of the Parole Board has directed the release of Mr John Worboys, following an oral hearing.
"The arrangements for Mr Worboys' release will be managed by the Ministry of Justice."