The Islamic State killer who has appeared on video beheading hostages has been named by media as former London computer programmer Mohammed Emwazi.
His name was first disclosed by the Washington Post, citing unidentified former associates, but two US government sources confirmed investigators believed Jihadi John was Emwazi.
He is reportedly from a middle-class family and earned a degree in computer programming before travelling to Syria in about 2012.
The Washington Post and BBC said Emwazi, in his mid-20s, was born in Kuwait but grew up in west London.
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According to reports, Emwazi moved to Britain at the age of six.
UK security forces reportedly chose not to disclose his name earlier for operational reasons. Police say they would not confirm or deny his identity because of their ongoing counter-terrrorism investigations.
List of killings began with journalist James Foley
Emwazi first appeared masked in a video in August when he apparently killed American journalist James Foley.
He was nicknamed Jihadi John after Beatle John Lennon due to his British accent.
He is also believed to have been responsible for the murder of American journalist Steven Sotloff, British aid workers David Haines and Allan Henning and US aid worker Abdul-Rahman Kassig.
Emwazi also appeared in a video with Japanese hostages Haruna Yukawa and Kenji Goto shortly before they were killed.
In the videos posted online, he appeared dressed all in black with only his eyes exposed and wielded a knife while launching tirades against the West.
Emwazi was identified to the Washington Post by friends and others familiar with the case, with one close acquaintance telling the paper: “I have no doubt that Mohammed is Jihadi John.”
He was described as quiet and polite with a taste for stylish clothes.
The International Centre for the Study of Radicalisation at London’s King’s College, a leading resource for studying foreign jihadists, said it believed the identity “to be accurate and correct”.
“The fact that Jihadi John has been unveiled in this manner demonstrates that whatever efforts are made, the ability to mask one’s identity is limited or in fact impossible and their true identities will eventually be revealed,” it said in a statement.
London’s Metropolitan Police, however, would not confirm the reports.
“We are not going to confirm the identity of anyone at this stage,” Richard Walton, head of the police counter-terrorism command, said in a statement.
British media had previously suggested the killer could be a different British jihadist.