Glenn Mulcaire accessed the new identities of individuals put under witness protection, but Scotland Yard took no action, it has been claimed.
BBC Panorama reported last night that the Metropolitan Police had evidence in 2006, during a previous investigation into phone-hacking, that Mulcaire had accessed the highly secret information.
It claimed that four of those targeted have only recently been told that they were victims, including Robert Thompson, who murdered James Bulger, and fellow child killer Mary Bell.
Ex-Metropolitan police officer Brian Paddick told the programme: "The Witness Protection Scheme is a very expensive operation to give people who've been convicted of very serious offences and people who are very vulnerable witnesses – to give them a completely new identity, so they can have a completely fresh start.
"For that information to get into the hands of journalists is potentially putting people's lives at risk"
The force insisted that there was no evidence to suggest an officer had leaked the information, and said that instead Mulcaire obtained the information via phone-hacking.
Injunctions protect the new identities of certain individuals, including Thompson.
The Attorney General will consider an alleged breach of an injunction by Mulcaire after all criminal trials linked to the current hacking and bribery investigations have finished.
A spokesman said: "In April 2012 the Attorney General's Office was notified by the Metropolitan Police that there was a potential breach of an injunction by Glenn Mulcaire.
"The Attorney General is responsible for taking action when certain injunctions have been breached, but as criminal matters are still ongoing, these cases take precedence."