It's taken 38 years, but the United Kingdom's government and military has officially apologized for Bloody Sunday, the 1972 massacre in which the British army opened fire on 28 civilians and killed 13 at a Northern Ireland Civil Rights Association march. On Tuesday, the results of the Saville report, the official report of the infamous incident commissioned in 1998, were released. The exhaustive probe—which cost £195 million ($289 million) and was the longest public investigation in U.K. history—culled statements from 2,500 witnesses and utilized over 900 oral testimonies. The inquiry reveals that none of the soldiers had fired in response to bombs or stone-throwers at the march, and that they had fired without warning. According to the report, some of those killed were very obviously trying to help others to safety, and soldiers even lied about their actions thereafter. British Prime Minister David Cameron called the conclusions "shocking" and said that he was "deeply sorry." General Sir David Richards, head of British army, said, "The report leaves me in no doubt that serious mistakes and failings by officers and soldiers on that terrible day led to the deaths of 13 civilians who did nothing that could have justified their shooting."