A rifle allegedly used by a loyalist paramilitary sniper to carry out some of the Ballymurphy killings was modified to fire the same type of bullets as British Army-issue guns, according to new information.
The Ulster Volunteer Force claims the weapon had been purchased in a Belfast gunsmith and recovered by police more than a decade after the August 1971 shootings.
A source close to the information process said the organisation may also be prepared to reveal information about other incidents where it was used.
Details have been passed to the Coroners Office ahead of an inquest into one of the most chaotic and notorious episodes of the Troubles.
Ten people were shot dead during three days of gunfire involving soldiers in the west Belfast neighbourhood.
The victims included a priest trying to aid one of the wounded and a mother-of-eight. Another man later died of heart failure.
Bereaved families have come to refer to the killings as the Ballymurphy massacre.
Members of the Parachute Regiment have always been held responsible for the civilians' deaths.
But last month the UVF claimed it was responsible for some of the shootings.
So-called "veterans" within the paramilitary grouping named Tommy West as the sniper they say opened fire from the nearby loyalist Springmartin estate during gun battles.
West, from the Shankill area of the city, is understood to have died of natural causes in 1980.
A second UVF member also allegedly acted as his "spotter".
At the time an interlocutor approached a lawyer to have the claims supplied to the coroner and police.
Assigned the anonymous title of Witness X, the interlocutor has now provided further information which went to the authorities last week. It includes claims that:
According to an informed source the UVF has also indicated the Mauser-type rifle was used in other shootings.
"They are prepared to release that information in the appropriate circumstances, and depending on how their input is received by the authorities," the source added.
So far, all of the claims have been passed to the Coroners Office by solicitor John Graham Greer, who is representing Witness X.
Mr Greer confirmed: "Further information has been provided to the coroner, but I'm not prepared to go into details at this stage."