Seamus Bradley was 19 when he was shot while running across a field in Derry.
He was killed by a soldier from the Royal Scots Regiment on 31 July during Operation Motorman.
Coroner judge Patrick Kinney said he believed the teenager was killed by a soldier who got out of a Saracen vehicle, dropped to one knee and opened fire.
“He was running across an open area of ground. He had no weapon. He was clearly visible and the fact he did not hold a weapon was clearly visible,“ he said.
“As he was running an army Saracen entered the same piece of ground.
“Almost immediately a soldier got out of the Saracen, took up a firing position and fired shots at Seamus Bradley ultimately causing his death. At the time of the shooting there was no other immediate or apparent threat to the soldiers in that area.
“I am satisfied that the soldier who fired the shots could not have held an honest belief that firing on Seamus Bradley was absolutely necessary to protect either himself or others from being killed or seriously injured.”
The coroner said he had not been able to confirm the identity of the soldier.
Mr Kinney said the soldier had breached the rules of operation in opening fire.
He added that the teenager could have survived if British soldiers had properly cared for him after the shooting.
“I find that if basic first aid had been provided to Seamus Bradley by the soldiers who collected him, and he was transported swiftly to hospital, he may well have survived his injuries,“ he said.
The coroner judge rejected the Bradley family’s claims that soldiers had tortured the teenager.
“In particular there is no evidence of strangulation, a broken neck or the use of barbed wire. There is no evidence that Seamus Bradley was hung on Bishop’s Field or that he was tortured at any stage,“ Mr Kinney said.
“I am satisfied that the force used was more than absolutely necessary in the circumstances.
“I therefore conclude that the use of force by the soldier who caused the death of Seamus Bradley was not justified.”
Around 200 former British military personnel are believed to be under investigation for alleged crimes, including murder, which took place during the Troubles.