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Members of the crowd carry pictures of the victims of Bloody Sunday while they march through Londonderry, Northern Ireland to the Guildhall where relatives of those killed on Bloody Sunday saw the first copies of the Saville Inquiry report on Tuesday. Image Credit: AP

London: Prime Minister David Cameron apologised on behalf of the British government Tuesday for the killings of 13 civilians by British troops on so-called Bloody Sunday, in Northern Ireland in 1972.

He told lawmakers that an investigation into Northern Ireland's biggest mass killing by British soldiers showed the attack was unjustified.

Cameron said the report shows there is "no ambiguity" about what happened that day, and that British soldiers fired first and even killed injured protesters trying to flee.

The prime minister said that the conclusions from the 12-year investigation were "shocking to read" and that he is "deeply sorry" for what happened.