It was the most notorious event of "the Troubles." Thousands of Catholics in Northern Ireland gathered in the city of Londonderry to protest London's policy of detention without trial for suspected IRA militants. The permitless and peaceful Sunday protest soon spiraled into violence when British paratroopers arrived on the scene. The ensuing bloodshed has been the inspiration for countless tributes, such as the U2 song, "Sunday Bloody Sunday." Doubt over whether there was any provocation in the crowd to justify the police action was finally put to rest by the Bloody Sunday Inquiry report, published on June 15, 2010. Cameron greeted the report from Parliament as spectators outside looked on by video (above) by saying the massacre was "unjustified and unjustifiable."