Relatives of the Catholic demonstrators shot to death by British troops on Northern Irelandís Bloody Sunday cried tears of joy Tuesday as an epic fact-finding probe ruled that their loved ones were innocent and the soldiers entirely to blame for the 1972 slaughter. The investigation took 12 years and nearly 200 million pounds ($290 million), but the victimsí families and the British, Irish and U.S. governments welcomed the findings as priceless to heal one of the gaping wounds left from Northern Irelandís four-decade conflict that left 3,700 dead. Thousands of residents of Londonderry Ė a predominantly Catholic city long synonymous with Britainís major mass killing from the Northern Ireland conflict Ė gathered outside the city hall to watch the verdict come in, followed by a lengthy apology from Prime Minister David Cameron in London that moved many locals long distrustful of British leaders. The probe found that soldiers opened fire without justification at unarmed, fleeing civilians and lied about it for decades, refuting an initial British investigation that branded the demonstrators as Irish Republican Army bombers and gunmen. Cameron, who was just 5 years old when the attack occurred, said it was ďboth unjustified and unjustifiable.Ē A young child, resting on a man's shoulders, holds a hanging effigy of a British soldier during a march in Belfast, capital of Northern Ireland, Feb. 1972. The rally follows the deadly shooting of 14 demonstrators by British paratroopers during the civil rights march. A young mother and son from the Bogside area in Londonderry, stop infront of a mural, Thursday, Jan 30, 1997, depicting a scene from Bloody Sunday. The event occured 25 years ago, when British Troops opened fire during a civil rights march and 14 marchers were killed.