Fifty years ago this month, Paratroopers shot dead 13 innocent civil rights marchers in Northern Ireland. It was the British Army's darkest day - forever known as Bloody Sunday. No soldier has been prosecuted. The tragedy helped fuel the IRA's bloody campaign over the violent decades ahead and set back the chances of peace for more than 20 years. Peter Taylor analyses what happened and why - and assesses Bloody Sunday's legacy today.
