The gruesome picture, believed to have been taken in the Isis stronghold of Raqqa, was captioned: “Chillin’ with my homie or what’s left of him.”
Bary reportedly travelled to the country last year from Maida Vale, west London, where he lived with his mother and five siblings.
His father Adel Abdul Bary, an Egyptian refugee thought to be one of Osama Bin Laden’s closes lieutenants, was extradited from Britain to the United States on charges of terrorism in 2012 for his alleged roles in the bombings of two US embassies in east Africa in 1998.
His family is frequently mentioned in rap songs that are still floating around the internet, with many people, unaware of L Jinny’s macabre transformation, praising his lyrics.
In early songs put online in 2012, Bary makes apparent reference to drug use, violence and life on a council estate and talks about the threat of his family being deported to Egypt.
“It’s hard to progress in the future with a damaged past but still I try to count my blessings and I thank Allah,” he rapped in 2012.
“I’m trying to change my ways but there’s blood on my hands and I can’t change my ways until there's funds in the bank.
“I can’t differentiate the angels from the demons, my heart’s disintegrating. I ain't got normal feelings."
“Even my life’s blessed, still I will not find rest.”
In later songs, apparent references to cannabis (“roll up and watch the leaves ignite”) stop and are replaced with tirades against people who choose to spend their money clubbing, drinking and on drugs rather than feeding their families.
The most recent video, which was posted on YouTube in March this year, is called “The Beginning”.
“Give me the pride and the honour like my father, I swear the day they came and took my dad, I could have killed a cop or two,” Bary raps.
“Imagine then I was only six, picture what I’d do now with a loaded stick. Like boom bang fine, I’m wishing you were dead, violate my brothers and I’m filling you with lead.”
Bary’s current whereabouts in Syria is not known and his Twitter account under the name “Terrorist” @ItsLJinny has been deactivated.
Previous posts mentioned Abu Hussein al Britani, a fellow Isis militant who has uploaded pictures of himself on Twitter with guns in Syria.
He and associate Abu Abdullah al-Britani were seen offering travel advice to would-be jihadists online earlier this year.
A sound expert who compared the footage of the brutal killing with Bary’s rap songs told the paper there was a “big likeness” between the voices.
Mr Foley’s murderer has not been identified by authorities but the Foreign Secretary said he sounded British and experts were urgently trying to trace him.
Police are believed to be preparing for raids on several homes across Britain in efforts to trace “jihadi John” but a spokesperson for the Counter Terrorism Unit at Scotland Yard would not confirm the identities of any suspects.
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