The masked man with the British accent in a series of gruesome beheading videos has been identified as Mohammed Emwazi from West London.
Former friends and colleagues confirmed his identity, while British authorities declined comment.
Emwazi was born in Kuwait and moved to London when he was six. The son of a mini-cab driver went on to graduate from the University of Westminster with a computer programming degree, and told friends that the British intelligence agency MI5 tried to recruit him.
Instead, he was placed on a terror watch list by the agency, and was barred from travelling to Kuwait, Saudi Arabia, and other Middle Eastern countries. He fled to Syria in 2012.
Emwazi first appeared in the Islamic State (IS) death video of American journalist James Foley, and is believed to have also executed Steven Sotloff, David Haines, Alan Henning, and Abdul-Rahman Kassig.
The terrorist, who is in his mid-20s, also appeared in the death videos of Japanese nationals Haruna Yukawa and Kenji Goto.
A British embassy spokeswoman declined to confirm or deny that Emwazi is "Jihadi John."
"Our prime minister has been clear that we want all those who have committed murder on behalf of ISIL to face justice for the appalling acts carried out," she told the Washington Post.
"There is an ongoing police investigation into the murder of hostages by ISIL in Syria. It is not appropriate for the government to comment on any part of it while this continues."
A former IS operative said he was certain that it was Emwazi on the execution videos.
"I knew it was him from his build and profile," the man said. "The people with me knew who he was too. But we could not ask questions. That would have been too dangerous. To us, he was the British guy who slaughters people."
