The Crown Prosecution Service examined sexual assault claims involving four alleged victims of Jimmy Savile in 2009 following an investigation by Surrey police.
On Monday, the CPS revealed for the first time that it reviewed assault claims involving more than one alleged victim while the Jim'll Fix It host was still alive.
Three of the alleged victims were aged under 16, including two pupils at the Duncroft approved school in Surrey in the late 1970s and a girl at the Stoke Mandeville hospital, where Savile was a regular visitor.
However, the investigation was dropped because none of the alleged victims would support a prosecution against Savile.
The CPS revealed more details about its own probe into Savile on Monday after a fresh examination of its evidence.
Surrey police passed details of three alleged victims to the CPS in 2009 after receiving an initial complaint from one woman in 2007. Sussex police passed the details of a further alleged victim to the CPS, taking the total to four.
Savile was interviewed under caution by Surrey police in October 2009, shortly after the alleged victims refused to support a prosecution. No charges were ever brought against the radio and TV presenter.
A spokesman for the CPS emphasised that the decision not to prosecute Savile in 2009 was taken due to insufficient evidence. It is understood that the CPS informed Surrey police of its decision to drop the case in October 2009, the same month it received the file.
In a statement, the CPS said: "A file was submitted by Surrey police to the Crown Prosecution Service in 2009 after a complaint was made by a woman who said she had witnessed an indecent assault by Jimmy Savile in the 1970s. Police conducted further enquiries and as a result the file which was submitted to the CPS also referenced three further potential offences involving Jimmy Savile.
"The original allegation was that Savile had indecently assaulted a girl under 16 at Duncroft children's home in the late 1970s. The three further potential offences were an alleged indecent assault on a girl under 16 at Stoke Mandeville hospital in or around 1973; an alleged incitement of a girl under 16 to engage in a sexual act at Duncroft children's home in the late 1970s; and an alleged indecent assault on an adult in Sussex in 1970.
"However, the evidence showed that none of the alleged victims would support a prosecution. In these circumstances, the CPS concluded that it was not possible to bring a prosecution in this matter."
The CPS said it did not have enough evidence to support a realistic prospect of conviction if the case against Savile was taken to a criminal court.
Surrey police spent more than a year from 2007 attempting to contact other former pupils of Duncroft school in an attempt to build up evidence against Savile.
One former Duncroft pupil contacted by police said she was kissed at the age of 14 by Savile; another reported that the BBC star had used inappropriate language.
The Metropolitan police has now identified more than 200 potential victims of Savile and is pursuing 400 lines of inquiry. The force has launched a criminal investigation into claims of sexual abuse by other living people.
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