No reasonable person would question that the Paras, who thought they were under fire from the IRA, carried out what Mr Cameron has called “unjustified and unjustifiable” killings when they shot dead 13 unarmed civilians during a civil rights march. But then the Paras were not the only ones guilty at that time. The IRA regularly carried out atrocities, such as the Bloody Friday bombings that killed 11 civilians in July 1972. But it is unlikely anyone in the IRA will face questioning over those murders, as most of those involved are now the proud recipients of letters from Tony Blair promising them immunity from prosecution.