A victim of black cab rapist John Worboys said she felt "cheated and betrayed" when she found out about his release and fears he could still be a danger to women.
She revealed that she found about about his imminent release, nine years after he was jailed, via a news website and had not been informed by the Parole Board.
The decision to release the 60-year-old has prompted anger from victims and questions around why not all of the 102 complainants had their cases brought to trial.
The victim said: "I never thought Worboys would see the light of day after the terrible offences he committed. I honestly thought he would never be allowed out of prison.
"So I was shocked, shaken and tearful when a friend sent me an email with a link to the story of his imminent release.
"I hadn't been told by the Parole Board and had to find out by looking at a news website which is completely out of order.
"I felt cheated and betrayed. They could have at least sent me a letter. "
A day after his release was confirmed, the Crown Prosecution Service (CPS) explained it had charged Worboys with offences "where it was deemed there was a realistic prospect of conviction".
The woman said: "I am really concerned that he could offend again. How can he carry out so many horrific crimes and then suddenly be ok?
"I feel like we need to know the reasons why the Parole Board think he is safe enough to release and whether he has admitted to any of the offences he wasn't convicted of.
"I think the police also need to investigate any other claims of women who have come forward so they too can get justice."
Another woman who said she had a narrow escape from Worboys said police had dismissed her when she reported an incident to them in 2002.
In a comment piece for the i newspaper, Hannah Roberts said it was six years on before she was given the opportunity to identify him and make a statement.
She said: "Many of the women who came forward to accuse Worboys were ignored or not believed by police at the time of their attacks.
"Now the same unheard women whose cases did not get to trial may feel slighted for a second time by suggestions that their cases did not meet the evidential test.
"The reality was that the police had accumulated a mountain of evidence that was not all needed for a successful outcome at trial and the CPS has to strike a balance between justice for victims and clogging up the courts for years."
Worboys, 60, was found guilty of 19 charges of drugging and sexually assaulting 12 women passengers, in one case raping a woman.
The CPS said 83 women had reported allegations up to the point of conviction, and a further 19 afterwards, and the body had advised officers to refer any allegations of rape.
One file was submitted in relation to an allegation of sexual assault but it "did not pass the evidential test", the CPS statement added.
It said: "It would be unlikely that it would be in the public interest to prosecute Worboys in relation to allegations of sexual assault or administering a substance with intent, because of the maximum sentence available to the court."
Chairman of the Parole Board, Professor Nick Hardwick, who apologised after some victims were not contacted ahead of the announcement that Worboys is to be released, will be summoned before the House of Commons Justice Committee to explain how the decision for release was reached.
The Metropolitan Police confirmed there is currently no live investigation into Worboys.