Mayor of London Sadiq Khan and two victims of the black cab rapist John Worboys have launched legal bids to keep him behind bars.
The formal application for a judicial review was lodged by the mayor on Thursday (January 25) after the controversial decision to release the serial sex attacker from jail.
Khan said he was fighting to put the "safety of Londoners and the needs of victims first" as preparations began for the High Court battle.
Two of Worboys's victims, known as DSD and NBV, lodged their own bid for a judicial review into the decision at the High Court on the same day as the mayor.
Worboys was jailed indefinitely in 2009, with a minimum term of eight years, for drugging and sexually assaulting his female passengers.
He was convicted of 19 offences against 12 women, however the true number of victims could be more than 100, with confirmed victims in Chelsea and the West End.
The Parole Board sparked fury earlier this month when it decided to release Worboys after he spent a decade in prison.
The victims' lawyer Harriet Wistrich said the raft of evidence she intends to hand to detectives "includes two previously unreported cases from 2002 and 2003 and two cases that were investigated by the police that would pass the evidential threshold but have not been prosecuted".
One of the women pursuing the judicial review, NBV, was a complainant in the criminal trial, while DSD was among the cases police decided not to prosecute.
"The two claimants who were not informed of the decision to release Worboys nor consulted on licence conditions are convinced that Worboys remains a danger to women," said the victims' lawyers.
"Their view is shared by many victims who have come forward recently, as well as the public at large.
"The claimants, who would much rather put this case behind them, consider they must do all they can to reduce the risk to other women and seek public accountability."
A previous review was ruled out by Justice Secretary and Lord Chancellor David Gauke.
The mayor said: "I have today lodged with the court an application for judicial review of the Parole Board's decision to release the convicted rapist John Worboys.
"It was an astonishing and deeply concerning decision that simply cannot go unchallenged. For victims, and all Londoners, it must be properly scrutinised in the courts. The chair of the Parole Board has welcomed this scrutiny.
"I will always put the safety of Londoners, and the needs of victims, first - which is why I instructed leading counsel to begin this process last week.
"Londoners need to know that those in authority are doing everything they can to keep them safe, and that means keeping dangerous individuals off our streets."
The 60-year-old has been transferred from HMP Wakefield in West Yorkshire to HMP Belmarsh in London, the city where the majority of his victims live.
Metropolitan Police confirmed on Tuesday that it is investigating a fresh allegation of historical sexual assault which is understood to have been made against Worboys.
The incident was said to have taken place in 1997 and was reported to police this month.
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