The Catholic Bishop of Down and Connor, Dr Noel Treanor, is due to release previously undisclosed church documents that relatives claim will strengthen demands for a public inquiry into the killings of 11 people by British soldiers in west Belfast in August 1971.
A Catholic priest and a mother-of-eight were among those killed by the Parachute Regiment in the Ballymurphy area.
The documents include eyewitness accounts taken two weeks after the killings.
Bishop Treanor said he was supporting calls for an independent international inquiry into the deaths and a British government apology.
The families of those killed made similar calls last month following the release of the Bloody Sunday Report into the deaths of 13 people who were killed by Parachute Regiment soldiers in Derry six months later.
The bishop will also call on the British and Irish Governments to discuss with the relevant institutions of the European Union their potential role in encouraging and supporting just and constructive ways of dealing with the past.
The shootings in Ballymurphy took place around the time of the introduction of internment.
According to the church, the accounts include a serving member of the British army, a member of the British navy who returned to his ship shortly after the shootings, and a former member of the Irish Guards.
In a statement, the church said: “Those who compiled the report indicate that on the basis of the eyewitness accounts, 'we are convinced that the British army units involved, whether through fear or vindictiveness, unnecessarily fired a large number of rounds into the waste grounds across which innocent men, women and children were fleeing'.”
It said the report found the people killed were not caught in crossfire. Soldiers at the time claimed they had exchanged fire with gunmen in the area.
