Londonderry, Northern Ireland ? Relatives of 13 Catholic demonstrators shot to death by British troops on Northern Ireland’s 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.

A man walks past a Bloody Sunday mural Tuesday in the Bogside area of Londonderry, Northern Ireland.

The investigation took 12 years and nearly $290 million, but the victims’ families and the British, Irish and U.S. governments welcomed the findings as priceless to heal one of the gaping wounds left from Northern Ireland’s four-decade conflict that left 3,700 dead.

Thousands of residents of Londonderry — a predominantly Catholic city long synonymous with Britain’s major mass killing from the Northern Ireland conflict — 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 “both unjustified and unjustifiable.”

“I couldn’t believe it, I was so overjoyed,” said Kay Duddy, clutching the handkerchief used to swab blood from her 17-year-old brother’s body that day. Jackie Duddy, the first of the 13 killed, was shot in the back.

“Never in my wildest dreams would I ever envisage a British prime minister would stand up in Parliament and tell the truth of what happened on Bloody Sunday,” Duddy said.

“David Cameron told the world and its mother that Jackie Duddy and the rest of the deceased and injured were innocent people. They were totally exonerated today,” she said.

One by one, relatives of the 13 dead and 15 wounded went to a podium, huge black-and-white pictures of their dead or wounded relative displayed on a massive television screen. Each declared their relief that the demonstrators were found innocent and the elite soldiers of the Parachute Regiment solely to blame.

“Thirty-eight years ago a story went around the world … that there was gunmen and bombers on our streets, and they were shot and killed. Today that lie has been uncovered,” said Kate Nash, whose 19-year-old brother William was shot fatally once through the chest.

Disturbing findings

The Bloody Sunday Inquiry, authorized by then-British Prime Minister Tony Blair in 1998 in the run-up to the negotiation of the Good Friday peace accord that year, was led by English judge Lord Saville. He gave the ex-paratroopers, now in their 60s and 70s, broad protections from criminal charges as well as anonymity in the witness box, citing the risk that IRA dissidents might target them in retaliation.

Some legal experts, however, said wiggle room remains for prosecutions and, more likely, civil lawsuits against retired soldiers, particularly because some of the them were found to have lied to Saville.

The 5,000-page report is based on evidence from 921 witnesses, 2,500 written statements and 60 volumes of written evidence.

Cameron apologized on behalf of the British government and summarized its findings: The soldiers never should have been ordered to confront the protesters, they fired the first shots and targeted unarmed people who were clearly fleeing or aiding the helpless wounded. None of those killed or wounded that day in Londonderry had posed a threat to the soldiers, Saville concluded.

Saville’s conclusions included damning new findings, including that soldiers fired twice at 22-year-old James Wray — once as he ran away, a second fatally after he was on the ground.

“As he lay there, defenseless and dying, he was deliberately shot again. The Saville report stated clearly that there was no justification for either of these two shots,” said his brother Liam.

The demonstrators were protesting the internment without trial of IRA suspects. The report said some soldiers fired knowing their victims were unarmed, and may have concluded all protesters were tied to IRA factions and therefore legitimate targets.

“It is at least possible that they did so in the indefensible belief that all the civilians they fired at were probably either members of the Provisional or Official IRA or were supporters of one or other of these paramilitary organizations, and so deserved to be shot,” the report said.