Two victims of black cab rapist John Worboys have joined the Mayor of London in mounting legal efforts to resist his controversial release.
The women, known as DSD and NBV, formally lodged an application on Thursday for a judicial review into the Parole Board's decision, their solicitors said.
Lawyers also intend to present police and prosecutors with a dossier of allegations against Worboys, saying they were contacted by a "number of other victims".
It came as Sadiq Khan launched his own legal battle at the High Court, saying he would fight to put the "safety of Londoners and the needs of victims first".
The Parole Board provoked fury this month when it directed Worboys's release after a decade in prison.
He was jailed indefinitely in 2009, with a minimum term of eight years, for drugging and sexually assaulting women passengers.
Despite being convicted of 19 offences against 12 women, it is feared Worboys may have more than 100 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.
Solicitors acting on behalf of the women said in a statement: "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.
"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."
Their application includes a request for urgent consideration seeking a stay of the release of Worboys.
They will claim that a decision not to disclose the Parole Board's decision to the public is unlawful, as it flies in the face of open justice.
"The second ground argues that the Parole Board decision is irrational on the basis of all known facts including: the long history of cold calculated attacks on a large number of women," the statement continued.
Mr Khan's decision to begin a legal challenge came after Justice Secretary and Lord Chancellor David Gauke ruled out a judicial review.
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."
Notorious predator Worboys has already been moved to a London jail ahead of his release, prompting outrage among his victims based in the capital.
The 60-year-old was transferred from HMP Wakefield in West Yorkshire to HMP Belmarsh, south-east London, at the weekend, it is understood.
On Tuesday, police said they were 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. Worboys has not been arrested.