Community leaders from the home town of jihadi Abu Sa'eed Al Britani say evidence suggesting he was imprisoned by Islamic State could deter other young Muslims from travelling to Syria.
Sky News has found his name scrawled on a wall of a prison in the recently liberated town of Raqqa, the one-time headquarters of IS.
Abu Sa'eed left for Syria in 2014 and is on a UN sanctions list.
He was prolific online and regularly posted videos and blogs from Syria denouncing the West and glorifying IS.
But there were clearly tensions within his life with the militants.
He wrote on a blog he missed his mum's cooking and foods like Jaffa Cakes and fish fingers.
Back in his home town, High Wycombe, community leader Mohammed Khaliel has been supporting his family.
He told Sky News: "He was a salesman for an extremist group - ISIS - and I think it's ironic that the very group that he was trying to attract others into have tortured him to death.
"I hope that speaks volumes to youngsters thinking of travelling to these dangerous parts of the world."
High Wycombe has been identified as an area where radicalisation is a problem.
Local mosques insist they are working to educate vulnerable young Muslims.
At the Wycombe Islamic Society mosque, where Abu Sa'eed worshipped before he left for Syria, they run a programme of youth classes.
Staff there described Abu Sa'eed as a "loner" and say he never spoke of his radical views or intention to travel to Syria.
Abu Sa'eed was dubbed the "Supermarket Jihadi" because he'd worked as a security guard in the local Morrison's.
Despite his many social media posts, we know he fell out with IS leaders who'd issued him a warning after he advised potential recruits to go to Libya and not Syria.
His last activity online was in July this year. The only clue as to what happened is a scratch mark bearing his name inside a notorious IS prison where inmates were routinely tortured and executed.
Terror analyst Milo Comerford, from the Tony Blair Institute for Global Change, said it is not uncommon for British jihadists to struggle with life in Syria.
He said: "Western Jihadis come with a preconception of what they would be doing.
"They thought that they would be fighting, they thought that they would be on the frontline of ISIS's crusade across Iraq and Syria, and actually the reality turned out to be very different.
"People are often put in positions of support, of cooking, they were untrained, they didn't have the military skills, and many were frustrated by this."