New DNA profiles and suspect fingermarks have been uncovered by detectives investigating the Army's notorious IRA agent Stakeknife.
Bedfordshire Police Chief Constable Jon Boutcher is investigating the high-ranking Army mole who reputedly led the republican organisation's "nutting squad", an internal security unit which brutally interrogated and murdered suspected spies during the Northern Ireland conflict.
Dozens of detectives are probing more than 50 murders. Suspects including members of the security forces and the Provisional IRA are being brought in for questioning.
In 2003, Stakeknife was widely named as west Belfast man Freddie Scappaticci, but he has always strongly denied the allegation.
The chief constable said: "We are using ground-breaking techniques to review and uncover forensic evidence which was not previously available and that has allowed us to drive this investigation further than has been previously possible.
"We have managed to obtain a number of new DNA profiles and unidentified finger marks which are highly likely to belong to offenders. This evidence is all helping us to piece together a picture of what really happened to allow us to finally get to the truth.
"This investigation has been hugely complex and, at times, challenging, but the team has been steadfast in its approach to gathering every possible piece of evidence."
The probe is centred on possible crimes by paramilitaries, agents and Army and police handlers linked to Stakeknife, allegedly the military's highest-ranking spy within the IRA.
Multiple murders, attempted murders, torture and unlawful imprisonments are included.
Earlier this month Scappaticci, 72, avoided prison after admitting two counts of possessing extreme pornography.
Operation Kenova, the name for the independent police investigation into Stakeknife, has gathered more than 12,000 documents, secured 1,000 statements and conducted 129 interviews with witnesses, victims and families resulting in more than 6,000 investigative actions for the team.
Mr Boutcher, who is leading the investigation, recalled: "I said at the outset that this would be a wide-ranging investigation and that is exactly what it has been.
"At the heart of the investigation and the reason we are doing this, are the families - without exception they have each shown incredible strength, bravery and humility in speaking to me and supporting Operation Kenova despite various setbacks and disappointments they may have had over the years.
"I made a promise to those families that I would do everything in my power to get the truth for them and that very much is what this investigation is about."
Most of those whom detectives have spoken to have been victims or witnesses but various suspects have been identified, the senior officer added.
Investigators based in London and Belfast also conducted full forensic reviews on numerous murder and abduction cases which have led to 199 requests for new forensic examinations, resulting in a number of new DNA profiles and suspect finger marks.
Mr Boutcher said he intended to submit full files to the Director of Public Prosecutions in Northern Ireland next year and appealed for anyone with information to come forward.
"These offences were committed by cowards and it's time the truth about those involved came out," he said.