Three psychiatrists submitted new reports saying Sergeant Alexander Blackman had an “Adjustment Disorder” after a stressful tour of duty in Afghanistan.
It substantially impaired his ability to form a rational judgment or exercise self-control, they said.
Professor Neil Greenberg told five senior judges at the Court Martial Appeal Court in London: “Everybody has their breaking point. “There’s no such thing as a Rambo, an Arnold Schwarzenegger, who can face all sorts of stress and appear invulnerable. That sort only exists in the cinema.”
- Footage of moments leading up to Marine A Taliban shooting released
- Marine in bid to overturn murder conviction 'faced austere conditions'
Sgt Blackman suffers from a mental disorder, an appeal court heard
Screenshot of footage recorded by a soldier’s helmet camera
Jonathan Goldberg QC, for Blackman, said he would not have felt able to admit to mental illness.
Everybody has their breaking point
Professor Neil Greenberg told court
He added: “He is a very reserved man. He is not a John Wayne character. He says little.
“He is proud of the Marines’ macho culture. It is not in their nature to be very forthcoming.”
Blackman, 42, from Taunton, Somerset, was convicted of murder in December 2013 and jailed for life with a minimum of 10 years.
A court artist sketch by Elizabeth Cook of Sergeant Alexander Blackman appearing via video link
Get Quotes on Home Insurance
Sgt Blackman's wife Claire was in the packed court, along with Marine veterans
It was reduced to eight years in 2014.
Blackman – who had denied murder, claiming he thought the Taliban was dead – watched the hearing via video link.
His wife Claire was in the packed court, along with Marine veterans and novelist Frederick Forsyth.
A harrowing video, recorded by a soldier’s helmet camera, was played of the moment Blackman shot the Taliban in the chest, saying: “Shuffle off this mortal coil, you ****. It’s nothing you wouldn’t do to us.”
Richard Whittam, QC, for the Crown, said Blackman shot the man after being told an Apache helicopter which could have witnessed the killing had flown away.
Remembering Afghanistan heroes Sun, March 15, 2015
The Queen and Britain's prime minister joined veterans in a service to commemorate the end of Britain's combat in Afghanistan.
PA 1 of 49
Prince Harry at the Afghanistan war commemorations
Novelist Frederick Forsyth attended court
But forensic psychiatrist Dr Philip Joseph said the shooting may have been “an impulsive act”.
He said Blackman told him he shot the insurgent in “an unthinking moment” and immediately realised he had made a mistake.
The court heard Blackman was rated a “superb” soldier but during his tour of duty seven men in 42 Commando had been killed, including two close colleagues, and 45 had suffered life-changing injuries.
He was described as “a husk of his former self”.
Prof Greenberg told the court: “He was suddenly presented with a situation in which aggression and anger which had been pent up could be released.”
The appeal continues.
- Review for killer Royal Marine of a wounded Afghan captive
- And still the Royal Marine waits to be awarded bail
- Royal Marines hero, 84, backs bid to free Marine A Alexander Blackman