As a convoy of Isis vehicles travels down a desert road, a young man proudly carries the black flag of jihad as he stands surrounded by Kalashnikov-wielding militants.
In slow motion, he leads the stream of fighters to a clearing where they go on to call on their fellow Europeans to join their jihad, before shooting two prisoners dead.
The man carrying the banner is Harry Sarfo, a former Royal Mail postman who went to school and converted to Islam in London, before entering a spiral of radicalisation that would eventually see him training as an Isis fighter in Syria.
The 27-year-old, who is currently in prison awaiting trial on terror charges after fleeing the group’s brutal regime, said the bloody reality was far from the jihadist fantasy presented in the videos that initially attracted him.
In a wide-ranging interview conducted with The Independent via his lawyer, he described his experience appearing in one of the group's notorious execution films.
“When they speak in their videos with weapons, it feels like they're calling you. We need you here! Our brothers and sisters need you! We bring peace, dignity and honour!” he said.
“But in reality it is all a lie - most videos are staged. People are telling other people to kill but themselves they don't fight at all. It's like a movie, everyone is playing their role.”
In the film Sarfo appeared in, titled Tourism in this Community, he was shown sitting in dappled sunlight among other fighters as a German militant vowed revenge on his home country for the Afghanistan war and urged followers to join them in Syria or launch attacks in Europe.
“If you cannot make hijrah to the Islamic State, then seek jihad in Germany,” a jihadist named as Yamin A Z tells the camera in German.
“Strike the infidels in their own homes, kill them wherever you find them.”
The next scene shows Yamin and Mohamed Mahmoud, an Islamist from Austria, standing over two kneeling prisoners in the ancient ruins of Palmyra, which have since been re-captured by Syrian government forces.
Vowing revenge on German Chancellor Angela Merkel, Mahmoud orders viewers to “pick up a big knife, go down to the streets and slaughter every infidel you encounter”.
He and Yamin then shoot both prisoners in the head with automatic rifles.
Sarfo, who was born in Germany but grew up in the UK, insists he never personally killed anyone but described witnessing countless executions and atrocities while being trained as a member of Isis’s “special forces” in Raqqa from April to July last year.
He recalled seeing six men shot in the head with Kalashnikovs and watching a man having his hand being chopped off and being forced to hold it in his remaining hand.
“Brother killing brothers - it is not just un-Islamic, it is inhuman,” he said.
“A blood-related brother killed his own brother on suspicion of being a spy. Isis gave him the order to kill him. Friends killing friends.”
Sarfo warned young people not to be deceived by propaganda claiming to show the “daily life of Isis".
The group has become notorious for gory footage showing the murder of foreign hostages and prisoners, but its extensive media network is careful to temper the extreme violence with rosy depictions of life under its rule and the promise of freedom for Muslim recruits.
Many videos show its militants surrounded by children, giving out sweets, or benevolently distributing food among the families remaining in its territories, while others attempt to portray friendship between fighters and their lifestyle under the protection of the "caliphate".
But Sarfo’s dominant memory from his four months living in the so-called Islamic State was one of astonishing hardship and brutality.
As well as regular stonings and beheadings, he described daily bombardment on bleak cities confined by checkpoints, where Sharia was enforced by Isis militants patrolling the streets with machine guns.
“Once there, you'll realise but it is too late to turn back”, he said in a plea to other young Europeans not to repeat his mistake.
“Women come to the Islamic State think it is a romance, that they will get married and live happily ever after. The reality looks different.
“No freedom locked up in a house, your child will be born to die for nothing. If your man dies, you will have to remarry if you want to see the sunlight again.
“If you try to leave, imprisonment and execution will be your fate.”
Sarfo urged young Muslims not to throw their lives away and let Isis “brainwash your mind and destroy your soul”.
He believes his role was to die in the group’s name, like other recruits he met from Britain, France, Belgium, the Netherlands, Scandinavia, Spain, Portugal, Austria and “many more” countries.
Sarfo is far from the only Isis fighter becoming disillusioned with the group’s ideology, sparking ruthless efforts to discourage deserters as air strikes and enemy operations threaten its hold on swathes of Iraq and Syria.
“Many have tried (to flee) but they are either dead or in jail waiting for executions”, he said. “Among them are a handful of British citizens. I spoke to some of them who wanted to leave - many say it is impossible.
“When you make it, you will get a life sentence in jail. Many have already been involved in fighting so they said there is no hope for them.”
Up to 800 jihadists are believed to have travelled from the UK to join other Isis and other Islamist groups in Syria and Iraq, with about half having returned. Whether they deserted their group or were sent deliberately is unclear.
As his disgust with the brutality of his new life mounted, Sarfo resolved to flee after his own study of the Koran led him to the realisation that Isis was “totally un-Islamic”.
"I came to the conclusion that this is not the path to paradise, it is the path to hell,” he said.
"I knew that if I died there I would never be able to enter the gates of paradise. Instead of freeing the Syrian people and uplift them, they've created another regime.
"I didn't want people to remember me that way and I knew that as long as I wasn't involved in any of these barbaric things I could return home and tell the world my story.”
Sarfo saw his opportunity while being treated for hepatitis C at a hospital in Tabqah, a city in Raqqa province, planning his escape from his bed.
He travelled to a succession of border towns, concocting story that his wife and children were imprisoned in Turkey to attempt to convince Isis militants to let him leave their territory.
But local officials refused, telling him other recruits had been using similar excuses to defect - a capital offence.
Coming clean to a taxi driver, Sarfo was told the way to the nearby Turkish border was littered with mines, snipers and militants. “I knew I would die anyway, so I had nothing to lose,” he said.
Sarfo says he was chased, shot at and forced to hide in mud for nine hours as he evaded Isis guards crossing fields to the border.
He made it safely into Turkey and flew back to his German hometown of Bremen, where he was greeted by police at the city's airport on 20 July.
A spokesperson for the German federal prosecutor's office said he has been charged with being an Isis member, undergoing firearms training and appearing in propaganda urging Germans to travel to Syria or launch attacks at home.
He remains in prison in Bremen awaiting trial.
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