A British soldier who killed a "totally innocent" teenager when he fired close to a crowd of youths was unjustified in discharging the fatal round, a coroner has ruled.
Manus Deery, 15, was killed as he stood in an archway near a chip shop in Londonderry socialising with friends in May 1972.
His sister Helen said her family's campaign for a new inquest had been vindicated by the coroner's ruling.
"We always knew Manus was innocent," she said.
The teenager, who had just started his first job two weeks before he died, was struck in the head by fragments of a bullet that ricocheted off a wall.
It was fired by a soldier from a fortified observation sanger high above the Bogside area on Derry's historic city walls.
Coroner Mr Justice Adrian Colton, who presided over a fresh inquest into one of the most contentious deaths of the Troubles, rejected the soldier's claim that he fired at a gunman.
During a time when IRA sniper attacks on the Army were commonplace, Private William Glasgow, now deceased, insisted he had fired on a man armed with a rifle, but missed and hit the wall.
Mr Justice Colton told Derry courthouse he had concluded there was no such gunman.
"The discharge of the round was unjustified," he said.
"Neither Manus nor anyone close to him was acting in a manner that could reasonably have been perceived as posing a threat of death or injury to Private Glasgow or any other person."
However, the coroner said he was unable to determine whether the Royal Welch Fusilier was under an "honest belief" that he had seen an armed man - citing his inability to question the late serviceman during the inquest.
"Even if Private Glasgow had an honest belief that there was a gunman present, the force used was disproportionate to the threat perceived and therefore more than was absolutely necessary in the circumstances," he said.
Mr Justice Colton said the Army's rules of engagement at the time - the "Yellow Card" - had not been adhered to.
"Private Glasgow was not justified in opening fire," said Mr Justice Colton.
The killing occurred months after the Bloody Sunday shootings in Derry, when soldiers killed 13 civil rights demonstrators and fatally injured another on the streets of the Bogside.
The coroner said the Deery family's pursuit of a new inquest was fuelled by a burning desire to wipe away a "perceived stain" on Manus's character related to insinuations he may have been involved in paramilitary activity, or had even been the gunman spoken of by Pte Glasgow.
Delivering his ruling in the non-jury inquest, he said he had "no doubt" the boy was blameless.
"Manus Deery was a totally innocent victim," he said.
"He didn't pose a threat to soldiers or anyone else."
During inquest proceedings, the Ministry of Defence (MoD) acknowledged that the shooting was unjustified.
In a statement given the day after the incident, Pte Glasgow claimed he fired at a gunman standing beneath an archway beside a pub in the Bogside.
He was not prosecuted.
A new inquest was ordered by Northern Ireland's attorney general John Larkin in 2012. The original inquest in 1973 returned an open verdict.
The coroner said official Army and police investigations of the shooting in 1972 were "flawed and inadequate".
Helen Deery, who long campaigned for a second inquest, said she was delighted her brother's name had been cleared.
"It has been a long, drawn-out process and there's been lots of hurdles along the way, but it's been worth it," she said.
"My emotions today are I love my brother, so I am just a bit sentimental and peaceful too.
"I'll probably go to the cemetery at some stage. But this was about Manus and all the witnesses and clearing all their names."
She said Manus was a "beautiful wee boy with his whole life in front of him".
"I hope other families will persist in justice and persist in truth and know that it can be done," she added.
The ruling was delivered as political parties at Stormont remain deadlocked over new mechanisms to deal with the legacy of the Troubles.
One initiative stuck in the starting blocks due to the impasse is a beefed up special unit within the coroners' service to deal with historic inquests.
Ms Deery was sceptical of the politicians' ability to deliver.
"Personally I don't think the politicians give a damn about the victims," she said.
"I have no faith in Stormont or the politicians."