The relatives have lobbied for an investigation similar to the one that explored 1972's Bloody Sunday, when troops shot dead 13 Catholic demonstrators in another city, Londonderry.
That 12-year probe concluded the soldiers killed unarmed civilians, not armed IRA members.
Britain's secretary of state for Northern Ireland, Theresa Villiers, said Britain didn't believe a probe "would provide answers which are not already in the public domain or covered by existing legal processes."