By Richard Allen Greene
BBC News, Washington
The US pilots who killed a UK soldier in a "friendly fire" incident in Iraq were cleared of wrongdoing by a US military investigation three years ago.
Matty Hull was one of six UK troops killed by friendly fire during the war
No-one involved in the incident was punished, the US Air Force has said.
"The pilots... believed they were engaging an enemy target, they were clearly remorseful and they had been given the all-clear by controllers."
"Miscommunications" and "the fog of war" were among the causes of the incident, the Air Force told the BBC.
The investigation was launched weeks after Lance Corporal of Horse Matty Hull, 25, was killed in March 2003, and results were handed to UK military officers in November of that year, the Air Force said.
But how would investigators have reached their conclusion?
Two questions would have been critical, experts say - did the pilots follow the rules of engagement issued by their commanders, and did "the fog of war" affect their decisions?
Unexpected and uncontrollable
The phrase "fog of war" crops up often in discussions of what happens on the battlefield.
Coined by the seminal 19th-Century military thinker Carl von Clausewitz, it refers to the myriad unexpected, uncontrollable factors which affect troops in combat.
And in the United States, it can be a mitigating factor when blame is being placed for wrongful deaths.
Ward Carroll, a former Navy pilot who is now editor of the website Military.com, reviewed the leaked cockpit videotape which has renewed interest in the death of Matty Hull.
He identified a number of variables that could have affected the pilot's decision to fire on what turned out to be British troops.
"The lead pilot asks the ground controller if there are friendlies [in the area]. He doesn't get an answer - two ground controllers are talking to each other. This is the fog of war."
The pilots were under both time pressure and geographical pressure, as the convoy appeared to be heading towards a village, where the pilots could not strafe them, Mr Carroll said.
The fliers are ultimately told there are no friendly forces in the area - although the ground controller admits he does not know as much about the situation as he would like, and at least one pilot spots orange panels on the British forces which should identify them as friendly.
"I can understand how this happens," Mr Carroll says.
"They were told there were no friendlies. They identified the orange panels but were told again there were no friendlies."
Pressure on pilots
The pilots, he said, would be trying to balance competing demands.
Matty Hull's unit was hit by an A-10 Thunderbolt
"If I am too cautious and we get a village taken out, the question would arise: 'Why did you not drop your weapons when you were cleared to fire?'"
On the other hand, he added, the pilot saw the signal that should have told him he was not looking at hostile troops.
"He sees the orange panels. Now he knows more than anyone else.
"This is a classic friendly-fire fog-of-war scenario: Bad intelligence, garbled communications, time and geography against the guys in the airplane. But at the end of the day, orange equals friendly - and you sit on your hands."
The leaking of the cockpit tape has spurred debate in the UK about the training US military pilots receive.
The pilots who killed Matty Hull - who have never been publicly identified - were Air National Guard fliers, not regular Air Force, and were reportedly on their first combat mission.
History of accidents
Friendly fire incidents are not all that uncommon - and have happened throughout history.
A US military study that examined wars from World War I to the first Gulf War found that 15% of all casualties came from friendly fire, according to retired US Army Lt Col James Corum, the author of Fighting the War on Terror.
The British and German military statistics were similar, the study found.
"These days, thanks to better communication and coordination, the incidents of friendly fire are far less common than before," he said.
"However, when they do occur, there are bound to be serious casualties due to the very lethal nature of modern precision weapons."
He said it was difficult to point to a single cause for most friendly fire incidents.
"In a lot of ways a friendly fire incident is something like a typical aircraft accident - there is a series of small mistakes that ends up in a fatal accident."
"The US and UK work very hard to avoid such things, but in a highly mobile operation with literally thousands of coalition and enemy vehicles in the area of operations some mistakes are bound to happen."
That will be little comfort to the family of Matty Hull.
It may also be little comfort to the pilots who killed him, Ward Carroll says.
"You can hear in their voices as soon as they realise what's happened. I wouldn't wish that on my worst enemy.
"These guys live in hell for the balance of their lives."
Have you been affected by this story? Do you or your family serve in the military? You can send us your experiences using the form below:
The BBC may edit your comments and cannot guarantee that all emails will be published.