A shadowy Special Branch ballistics unit is being investigated over its links to weapons used in 60 murders.
The revelation is made in Tuesday night's BBC Spotlight NI programme.
It looks at the Weapons & Explosives Research Centre (WERC) which was the Special Branch ballistics unit up until 2009.
WERC was run by Special Branch to gather intelligence from weapons to trace them and link them to killings and paramilitary groups.
But it also aided Special Branch in another way.
It would deactivate guns handed over by informers and then they would be returned to arms dumps. But sometimes the guns would be reactivated by the paramilitary groups and used to kill.
Paul Holmes, director of the Ombudsman's Historic Investigations unit, told Spotlight it currently had "four complex criminal investigations ongoing".
"In each of those investigations, we are examining issues around the activities of WERC and weapons that were used to kill over 60 people," he said.
"Principally members of the public, however, we have increasingly become aware of allegations that a number of members of the security forces were also murdered by weapons that had been at one point or another in the hands of WERC."
Spotlight discovered that a Special Branch WERC officer saw two IRA guns being brought in for test firing and then returned to the IRA arms dump in full working order. They were subsequently used to kill two beat officers in Belfast.
The Special Branch WERC officer did not name the two officers, but Spotlight searched the records of every police officer killed during the conflict.
We believe we have identified the Royal Ulster Constabulary (RUC) officers who were killed with these guns as Constables Gary Meyer and Harry Beckett, who were shot dead in June 1990.
Constable Beckett's daughter Kathryn read the Special Branch officer's statement.
She said it made her feel "physically sick".
"I am horrified, these were my father's colleagues, employers, and they did this and allowed this to go on," she said. "Their actions in my view caused his death."
Kathryn told Spotlight that there was further tragedy in her life as she recalled her mother's reaction to the loss of her husband. She was just 17 at the time.
She said: "They had been together since they were 17 or 18, they had been married at 21.
"They were each other's true halves.
"Her heart just shattered and five months after my dad's death my mum died. The coroner said in the inquest basically it was she died of a broken heart. I didn't lose one parent that day at 17, I lost both."
Kathryn wants tough action against those she feels were involved in allowing her father to die.
"I would like to know who sanctioned it, I would like them to sit and look me in the eye and explain to me why I have not got a father and what right that they have to let this happen," she added. "And I would like them to be made fully accountable in a court of law."
We asked the Police Service of Northern Ireland (PSNI) to talk about the practices of Special Branch and WERC, but they declined to take part or offer us a statement.
You can see the full story on Spotlight on Tuesday night at 22:45 BST on BBC One Northern Ireland.