Media playback is unsupported on your device Media caption Sgt Blackman's murder conviction has now been reduced to manslaughter

As the conviction of Sgt Alexander Blackman for shooting an injured Afghan fighter in 2011 is reduced from murder to manslaughter on the grounds of his mental illness, Royal Marines who fought alongside him have spoken for the first time - offering new insights into the killing.

In interviews for BBC Panorama, the men from 42 Commando said they wanted the insurgent dead and their comrade "took one for the team" when he faced a court martial.

His colleagues said they also suffered from post-traumatic stress and one marine believes such incidents occurred elsewhere during the conflict.

There is much public sympathy for Blackman, 42, but few people who have watched the full video of the killing - recorded by another marine's helmet-mounted camera - would describe him as a hero.

The footage has not been made public but Blackman can be heard trying to cover up his actions, making sure a helicopter above is out of sight before he delivers the fatal shot.

Perhaps more understandable though is the sympathy of the men who fought alongside him and endured the same hardships.

'Sending out a signal'

Colleagues suggested there were other pressures on Blackman, who was known as Marine A during the original trial process and was only fully identified when he was convicted.

Rob Driscoll, who was at a nearby patrol base at the time of the killing, told Panorama: "Everyone that was speaking on that radio was sending out a signal to Al... everyone wanted that guy to be dead."

He said no-one would have wanted to send out a medical team to help the insurgent because the ground could have been littered with roadside bombs, while a helicopter might have been targeted in the air.

They would have done it for one of their own, but risking British lives for a wounded Taliban fighter "who has been shooting at them for the last four months" was less appealing, he said.

Image caption The helmet-mounted camera of another marine filmed Blackman (pictured) shooting the prisoner

Sam Deen, who was on the patrol, said: "I do remember saying, 'yeah I would shoot him'... and I do think I influenced what happened".

"A few of the other lads said that," Mr Deen said.

The killing, on 15 September 2011, took place after a patrol base in Helmand province came under fire from two insurgents.

'Successful day'

One of the attackers was seriously injured by gunfire from an Apache helicopter sent to provide air support, and the marines found him in a field.

The footage from the helmet-mounted camera showed Blackman shooting the Afghan prisoner in the chest at close range with a 9mm pistol.

Blackman, from Taunton, was convicted of murder in November 2013 and jailed for life. He lost an appeal in May of the following year, but his 10-year minimum term was reduced to eight years.

Five judges at the Court Martial Appeal Court in London have now ruled the conviction should be manslaughter on the ground of diminished responsibility, not murder.

A further hearing will now decide what sentence Blackman should serve.

Media playback is unsupported on your device Media caption Extract from helmet camera audio recording of incident in Helmand

Filmmaker and anthropologist Chris Terrill was embedded with Blackman's unit at the time of the shooting.

His film for Panorama tries to look beyond the narrow focus of the helmet camera that led to Blackman's conviction and questions whether, in the slow attrition of war, they began to think as a pack and lose their moral compass.

Speaking about Blackman's decision to kill the insurgent, Sam Deen says: "I do think he took the responsibility for the younger lads… he thought it was his responsibility to do it, and then move on."

Rob Driscoll admits to some sleepless nights but adds: "I'm glad Al did what he did because all my guys went home".

Louis Nethercott, another Royal Marine on the patrol, tells Panorama: "I think it was just another day in Afghanistan and that's the way it goes out there.

"And none of us got hurt so it was a successful day as far as I'm concerned".

Chris Terrill asks another Royal Marine who was on that tour whether he thought this was the only time such an incident occurred during the Afghan war.

His answer - "No".

Panorama, Marine A: The Inside Story will be on BBC One at 22:50 GMT, and available later on iPlayer.