This is the moment a group of drunk, topless marines twerk and sing karaoke two hours before one of them kills a man with a single punch.

Commando Joseph Jones, 23, left Cemal Yilmaz's jaw broken and with three knuckle prints when he attacked him on December 12 last year outside a bar in Exmouth, Devon.

Jones, from a family of boxing enthusiasts, walked away after hitting Cemal, a 29-year-old chef, who was unconscious before his head hit the pavement and died three days later in hospital from a bleed on the brain.

The marine was convicted of manslaughter in March this year and sentenced to three and a half years behind bars.

Cemal's family were devastated by the sentence, which they described as a 'total insult to their son's life', but even more disturbed to learn last month Jones would be eligible for release in August next year - earlier than the judge initially indicated.

His mother, Ann-Marie, told the Daily Mail: 'It's disgusting, disgraceful, degrading. Throughout the whole process, we were told to keep quiet, not to speak out.

'It feels like everyone has sided with Jones and it's been swept under a rug because he's a marine. But he killed our son.

'We haven't had any apology from the marines, no one has visited the house. And mistakes by the justice system along the way have only made things worse.' 

Footage has now emerged of Jones and his fellow marines from earlier that night, two hours before he delivered a 'fast, jab-style' killer punch to unsuspecting Cemal.

The group was evidently in full party mode, bouncing and swaying around a stage with their tops off, under the red neon lights of one of Exmouth's bars.

Jones, circled in red in the video, grabs a microphone and launches into a rendition of B*tch by Meredith Brooks with a partner, before two of his commando pals grab his shoulders from behind.

At the end of the clip, one of the men says into the mic: 'Jones, I love you Jones.'

Footage then shows a topless man, who appears also to be a marine, twerking on another man in the same area, before bending down further as his friend smacks his bottom.

Two hours later, Jones, of Wolverhampton, was asked by Cemal outside a pub whether he was from Birmingham.

As Cemal turned away to speak to a friend, Jones lamped him on the jaw, explaining to an onlooker he had felt 'disrespected' by the question.

Prosecutor Lee Bremridge said Cemal was a 'larger than life character' and well-known in the shops and pubs of Exmouth.

He added that Jones 'used violence to a man who was just no threat to him at all', and that marines were supposed to be trained to use judgement and restraint.

Jones eventually pleaded guilty to manslaughter after it emerged there were 155 witness statements that would otherwise be read out in court.

But the sentence provided no solace to Cemal's family.

Jones was told in court he would have to serve at least two-thirds of his 42-month sentence, which would see him behind bars until July 2028.

So it was with horror that Ann-Marie opened a letter last month explaining he would actually be eligible for release in August 2027, and that he was being moved to a category D prison.

Inmates in these prisons may be permitted to spend time out in the community, although Jones is not currently able to do so. 

The Daily Mail understands the judge made a mistake in saying at least two-thirds of the sentence would have to be served.

The Yilmaz family applied to have Jones' punishment reviewed under the Unduly Lenient Sentence scheme, but it remained unchanged.

Another blunder meant that decision was not communicated to Ann-Marie, as she had not been down as a next of kin.

Ellie Reeves, the Solicitor General for England and Wales, wrote to her to apologise, admitting it was 'not acceptable' and a 'very unfortunate oversight'. 

Remembering her son, an emotional Ann-Marie said: 'He was just such a lovely lad, he would give you the shirt off his back.

'There were 500 people at his funeral, which shows just how much people loved him.

'We get 80-year-old couples coming into our kebab shop and sobbing their hearts out because he showed them so much kindness. He used to go round to their houses and give them food.

'I burst into tears when the sentence was read out. None of it made any sense.'

Recalling the traumatic night, she said: 'Cem just asked him, was he a Brummie? He had a Birmingham accent. He said: "No, I'm from Wolverhampton."

'Cem just said: "Oh right, OK," before he turned, and the next thing he was punched so hard. 

'The whack was so loud and he fell unconscious to the floor and smacked his head on the concrete.

'Cem had turned to talk to another guy and did not see the punch coming. It was horrendous. He had a massive haemorrhage and was rushed to hospital.

'We were put into a side room and a doctor came over and said there was nothing we could do. The bleed was that massive. He had fractured the back of his head and was bleeding from the right ear.

'If Jones was a decent Royal Marine he wouldn't have punched him, or left him on the floor and walked away. He was asked why he did it and just said: "Because he disrespected me," then walked off and left him for dead.

'They are taught how to kill with their hands, but are meant to protect people in this country, and should know so much better.

'I had to watch my son on a life support machine with three knuckle marks on his chin - just because he called this coward a Brummie. It is just a term and a phrase that people use all the time.'

A government spokesperson said: 'This was a tragic crime and we express our sincere condolences to the family and friends of Cemal Yilmaz.

'Victims deserve the support they need to rebuild their lives and we’re reviewing how we can make it easier for them to raise concerns about offenders' licence conditions.

'Prisoners are only moved to open jails after a careful risk assessment and must obey strict rules to remain there.'

A Royal Navy spokesperson said: 'Our thoughts remain with the family and friends of Cemal Yilmaz following this tragic incident. 

'We hold our people to the highest standards and will take appropriate action, including dismissal from the Royal Navy, against anyone who fails to uphold these high standards.'