Members of the IRA have come forward and said they were present when people were being tortured, the officer leading the Stakeknife investigation said.
People who owned premises where victims were detained have also spoken to independent detectives.
The IRA’s so-called nutting squad was an infamous unit which abducted those whom it suspected of being informers to the state and inflicted great cruelties on them at remote locations.
Bedfordshire Chief Constable Jon Boutcher is investigating the Army’s alleged mole in the republican organisation, Stakeknife, who led the nutting squad.
He said: “There was no intention to get the truth, these people were brutalised in ways that I in my 35 years as a detective have never seen that level of unwarranted violence.
“There is nothing noble or justified or right in what happened.
“Nothing can in any way justify what these people did and it is time that those families were given the truth and Kenova (the police investigation) is a chance to do that.”
Mr Boutcher added: “We have spoken to members of the IRA who have come forward and told us that they were present when people were held, when people were tortured, and have named the people involved.
“I am now bringing in all those people that I think were responsible for offences.
“I want to get those people who still know something, who felt that Kenova would just get closed down, or that Kenova would never result in any prosecutions, who now see things differently, who are beginning to have more confidence that Kenova is going to deliver on promises we made, to do our best to investigate things.
“We want those people to come and speak to us, to call us, to come and meet us, to listen to how we deal with things.”