The US soldier who killed aid worker Linda Norgrove during a botched rescue mission in Afghanistan made a "critical decision in a fraction of a second", a coroner has found.
Wiltshire coroner David Ridley recorded a "narrative verdict", which does not apportion blame to any one individual.
Earlier he said a verdict of accidental death would not "sit comfortably".
Ms Norgrove was kidnapped in Afghanistan and died during a failed rescue attempt on 8 October last year.
The 36-year-old aid worker, from Lewis in the Western Isles, was taken hostage in September 2010 and died during a US special forces operation.
A joint UK and US military investigation found that she was killed by a grenade thrown by one of her rescuers during fighting with her captors.
At the inquest in Trowbridge, Wiltshire, Mr Ridley paid tribute to the courage and bravery of the US forces for attempting a rescue on that night, and to Ms Norgrove for being in Afghanistan.
He found that a bullet wound to her leg sustained during the rescue was not a contributory factor in her death.
Mr Ridley said it was easy to criticise actions from an armchair.
Giving his verdict, Mr Ridley said: "What I've drawn from this hearing is that the operative genuinely feared for the safety of the lives of his colleagues and also himself and had to make a critical decision in a fraction of a second, unaware of Linda's presence."
After the hearing, Ms Norgrove's father John said the inquest confirmed what he had previously heard at a military briefing in October.
"We think that it's very creditable of the American authorities to accept that mistakes were made and to instigate an investigation, which we've found to be very full and thorough," Mr Norgrove said.
"On the actual night in question, a series of chance events all went the wrong way, one after another after another, and there appears to have been an error of judgement by one soldier in an action which lasted under a minute.
"One tragic aspect of it at that point was that when the grenade was thrown, it would appear that the kidnappers were all dead or dying and the only person who was absolutely killed by the grenade was Linda."
On Tuesday, the first witness to give evidence was senior British officer Brig Robert Nitsch, who was involved in the joint probe.
He said the soldier who threw the grenade, identified only as TM 5, had been "shattered" by the death of Ms Norgrove.
He was the most junior member of a group sent to rescue the 36-year-old after she was kidnapped.
Brig Nitsch said the soldier was mature, experienced and had used two grenades on a previous operation.
Commenting on the attempt to rescue Ms Norgrove, the British officer said the use of grenades was "inadvisable in retrospect" but entirely understandable.
He said TM 5 had been fearful for the safety of the rest of his team.
The inquest heard that visibility was poor and the rescue team did not see Ms Norgrove until she was found dead several minutes after the start of the operation.
It was initially said she had been killed by one of her captors.
Brig Nitsch said: "The team leader, in a previous tour of Afghanistan, has witnessed an insurgent blowing himself up in front of him.
"In his mind, that is what has happened here.
"(This was) one of the contributing factors why it wasn't confirmed until later that Linda was killed by this grenade rather than by a suicide vest."
Brig Nitsch said the team leader's mistaken belief contributed to the "false information given to the family and put in the public domain".
He said during the joint investigation into the operation there was no attempt to hide what had happened. He said he was struck by the integrity of the US special forces.