Three judges at the Court Martial Appeal Court in London, who heard arguments yesterday on behalf of Sergeant Alexander Blackman that his conviction should be quashed, will give their decision at a date to be fixed.
Lord Chief Justice Lord Thomas, Sir Brian Leveson and Lady Justice Hallett will rule on whether or not the conviction can stand.
In the event of the court finding against him on the conviction appeal, the judges have been urged to reduce his “manifestly excessive” sentence.
After being convicted last November at a court martial in Wiltshire, the 39-year-old was ordered to serve a minimum of ten years before he can apply for parole.
He was also “dismissed with disgrace” from the Royal Marines after he had served with distinction for 15 years, including tours of Iraq and Northern Ireland.
The killing happened in Helmand province in 2011 while Blackman, who is known as Al, was serving with Plymouth-based 42 Commando.
He shot the Afghan, who had been seriously injured in an attack by an Apache helicopter, in the chest at close range with a 9mm pistol before quoting a phrase from Shakespeare as the man convulsed and died in front of him.
Blackman told him: “There you are. Shuffle off this mortal coil, you c***. It’s nothing you wouldn’t do to us.”
He then turned to comrades and said: “Obviously this doesn’t go anywhere, fellas. I just broke the Geneva Convention.”
During the trial, Blackman was known as Marine A, and his junior colleagues – who were both cleared – as Marines B and C. They were later named as Corporal Christopher Watson and Marine Jack Hammond.
The shooting was captured on a camera mounted on the helmet of Cpl Watson.
Blackman, who denied murder, said he believed the victim was already dead and he was taking out his anger on a corpse. He has said he felt ashamed at his behaviour, describing it as a “stupid lack of self-control and lapse in judgment”.
His QC, Anthony Berry, said he was convicted by a seven-man court martial board. In explaining a point of law raised in the challenge, he said: “The appellant submits that the possibility that he was convicted by a simple majority renders his conviction inherently unsafe.”
He argued that “by virtue of the possibility that he was convicted by a simple majority of a seven-man board there remains doubt as to whether the prosecution in fact satisfied the criminal standard of proof.”
Mr Berry said it was also submitted that voting requirements in Crown Court constituted important procedural safeguards that are “unfairly denied” to those subject to the court martial process.
But Philip Havers QC, making submissions on behalf of the Defence Secretary, submitted that the challenge was “misconceived”.
At the completion of legal argument, Lord Thomas said the court would take time to consider the appeal.
No date was given for the ruling.