William McClelland was part of a three-man Loyalist paramilitary gang who were convicted of the murder of Rodney McCormick and John Turnley in 1980.
Brothers Robert and Eric McConnell were part of the gang convicted for their part in the murders.
During the 1982 trial Robert McConnell claimed he had been working for the SAS, saying they supplied him with weapons, uniforms and listening devices. That makes whether the accused had been in the British army significant.
The revelation comes on the back of last month’s news that British intelligence was involved in the Shankill bombing in 1993.
John Turnley was active in the National H-Block Committee against the withdrawal of political status from Republican prisoners.
Other members of the committee killed around this time included Noel Lyttle, Ronnie Bunting and Miriam Daly. Former Mid-Ulster MP Bernadette McAliskey was also seriously injured in a loyalist gun attack.
It was alleged at the time the SAS were directly involved in the attacks.
In a statement, Rodney McCormick’s son Rory said, “At no stage following the arrest, prosecution or conviction of these three individuals was the family told that one of the suspects had been a member of the UDR from mid-1975 until late 1978,” he said.
“This was withheld from us, along with the Turnley family, the press and the public.”
Paul O’Connor from the Pat Finucane Centre said that when he wrote to the police last year he was told “there is no information held by Legacy Investigation Branch to indicate that McClelland was a member of the armed forces, UDR or the Prison Service”.
“Last week, following months of repeated enquiries with the Ministry of Defence in London, we received official confirmation that McClelland had been in the regiment.”