MI5 is to be asked to set out what it knew about the activities of Stakeknife, a high-level British mole who operated inside the IRA.
A report in the Sunday Times revealed that the security service will be asked to provide police with a statement detailing its knowledge of crimes committed by Stakeknife, said to include up to 17 murders.
It follows the discovery of a cache of secret documents at MI5 headquarters in London by police officers from Operation Kenova.
The £35m probe launched in June 2016 is investigating a range of alleged activities including murders, kidnaps and tortures linked to Stakeknife dating back to the 1970s.
Operation Kenova - led by Bedfordshire Police Chief Constable Jon Boutcher - is investigating whether MI5 intelligence handlers took no action to prevent 17 IRA murders in order to protect the identity of their valuable agent.
Led by Stakeknife, the IRA's internal security unit, known as the 'nutting squad', is believed to have murdered at least 53 people that it claimed were informers between 1978 and 1995.
A source told the Sunday Times that Kenova had uncovered documents "which are very telling about the role that our man played in certain things".
"They are documents that the service has kept that they probably should have got rid of. Boutcher has upset quite a few people at the service.
"He is not in a cosy relationship with them. The victims' families are his priority.
"People were doing things that may have been deemed operationally necessary at the time, but may no longer be acceptable," the source told the newspaper.
It has been widely reported that Belfast man Freddie Scappaticci was Stakeknife. Former bricklayer Scappaticci (72), who now lives in England, denies the allegation.
Last week Scappaticci appeared in a London court charged with possession of extreme pornography, including images of animals. He pleaded guilty and was sentenced to three months' imprisonment, suspended for 12 months.
Mr Boutcher said Scappaticci's conviction was secured after material was seized as part of Operation Kenova. A team of more than 50 detectives is involved in the inquiry, which is expected to last at least five years.