Black-cab rapist John Worboys could be freed within weeks after the Government opted not to challenge his release.
Justice Secretary David Gauke said it would not be appropriate to seek a judicial review of the case after taking "considered and expert" legal advice.
An outcry erupted earlier this month after the Parole Board directed the release of Worboys, 60, after a decade behind bars.
He was jailed indefinitely in 2009, with a minimum term of eight years, for drugging and sexually assaulting women passengers.
Worboys was convicted of 19 offences against 12 victims but has been linked to more than 100 complaints in total.
Last weekend it emerged Mr Gauke had commissioned advice on the possibility of taking the highly unusual step of seeking a judicial review.
The Ministry of Justice had said he would only proceed "if there is a reasonable prospect of success".