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Blackman was previously tried under the name Marine A and his case has precipitated a groundswell of public support DANIEL LEAL-OLIVAS/AFP/Getty Images

Sgt Alexander Blackman, formerly known as Marine A, the British serviceman convicted of murder for the 2011 killing of a wounded Taliban soldier in Helmand Province, has been sentenced to seven years for manslaughter after his conviction was reduced to manslaughter on grounds of diminished responsibility.

The ruling means he could walk free within two weeks as he has already served three and a half years for his initial murder conviction.

In November 2013 Blackman became the first British serviceman to be convicted of murder on a foreign battlefield since the Second World War.

The 42-year-old from Taunton, Somerset, was originally handed a life sentence with a minimum of 10 years in prison, through this was later reduced to eight.

On 15 March this year Blackman's conviction was reduced from murder to manslaughter after a court heard fresh evidence about his mental state when he killed the wounded Taliban soldier.

A panel of five judges, led by Lord Chief Justice John Thomas, heard Blackman's appeal during a two-day hearing in February. They heard psychologists claim that the marine was suffering from combat stress disorder when he pulled the trigger.

Jonathan Goldberg QC argued that this new evidence meant Blackman's conviction should be quashed on grounds of diminished responsibility.

The court heard that Blackman had a history of depression and had succumbed to feelings of isolation while in Afghanistan. He was also affected by an earlier grenade attack that nearly killed him.

During a 2011 tour of Helmand, Province Blackman shot a wounded Taliban fighter in the chest with a 9mm pistol at close range. Video footage of the incident showed Blackman taunting his victim as he killed him. He said: ''There you are. Shuffle off this mortal coil, you c***. It's nothing you wouldn't do to us.''

After discharging his weapon, he added: ''Obviously this doesn't go anywhere, fellas. I just broke the Geneva Convention.''

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Blackman's wife Clare said she was "delighted" with the Appeal Court verdict on 15 March

Sergeant Rob Driscoll, who was on operation in Afghanistan at the time of Blackman's offence, told the Daily Telegraph that Blackman should never have been charged with murder: "I genuinely don't think that it ever should have happened. I just don't understand why he has been so badly treated and I am anxious to see how he will be treated now.

He added: "I think that it has all had a really significant impact on efficiency of our Armed Forces. There are young lads still in the Marines that will have these considerations to make and I am not sure how that will affect our operational capability."