The British Islamic State militant known as "Jihadi John" may have been killed in a US airstrike in Raqqa, Syria, this week.
His death has not been confirmed yet, but a senior administration official told The Daily Beast that the US is "pretty damn sure he is dead."
"Jihadi John" has previously been identified as Mohammed Emwazi, a 27-year-old who lived in London before joining ISIS.
Emwazi, who is believed to be responsible for multiple executions of Western hostages, reportedly became radicalized after run-ins with British intelligence officials, according to The Washington Post.
But it's unclear whether UK security services inadvertently radicalized Emwazi or simply recognized his potential for radicalization.
"Jihadi John" has appeared masked, but speaking with his British accent, in ISIS hostage-beheading videos, leading some who knew him before he left for Syria in 2012 to identify him to the newspaper.
Earlier this year, The Guardian confirmed Emwazi's identity as "Jihadi John," and two US government sources confirmed the same to Reuters.
Emwazi was reportedly born in Kuwait. He was from a "well-to-do" family, lived in London, and was described as polite and stylish. He is also educated, with a degree in computer programming, according to the Post.
His family — including Emwazi's parents, Jasem and Ghaneya, and sister — reportedly moved to the UK when Emwazi was six years old, according to CNN. His father reportedly worked as a taxi driver while his mother stayed home to care for the children.
People who grew up with Emwazi told British news organizations that he was a popular "boy next door" who liked football, pop music, and The Simpsons, according to CNN.
Emwazi occasionally prayed at a mosque and was known to adhere to his faith while he lived in London, but it wasn't until he planned a post-college graduation safari trip to Tanzania that he started to radicalize, sources told the Post.
He and two friends were detained in mid-2009 once they landing in Dar es Salaam. They were then held overnight and then deported, according to the Post.
Emwazi claimed that a British intelligence officer accused him of trying to travel to Somalia, where the militant group Al Shabab, an ally of Al Qaeda, is based.
Emwazi later returned to his native Kuwait and got a job at a computer company. He landed on the radar of British intelligence officials again in 2010, when they detained him and searched his belongings the day before he was due to fly back to Kuwait. He was prevented from returning there.
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He wrote in an email to Qureshi that he felt "like a prisoner ... a person imprisoned & controlled by security service men, stopping me from living my new life in my birthplace & country, Kuwait."
One of Emwazi's friends told the Post that he was "upset and wanted to start a life elsewhere" outside of London. "He at some stage reached the point where he was really just trying to find another way to get out."
Emwazi was also reportedly unable to travel to Saudi Arabia, where he wanted to teach English.
Around this time, other signs of his radicalization started to show. When a court in the US sentenced an Al Qaeda operative who murdered Americans in Afghanistan, Emwazi reportedly said that he "heard the upsetting news regarding our sister," noting "this should only keep us firmer towards fighting for freedom and justice!"
The last contact Qureshi reportedly had with Emwazi was in January 2012.
Qureshi said: "This is a young man who was ready to exhaust every single kind of avenue within the machinery of the state to bring a change for his personal situation." He said he thought "actions were taken to criminalize [Emwazi] and he had no way to do something against these actions."
However, some journalists and experts are raising doubts about the notion that security services were the defining factor in Emwazi gravitation toward ISIS (aka IS, ISIL, Daesh):
WaPo interpretation of Emwazi's trajectory reminds of Scahill on Awklaki. State pressure -> radicalisation. Not sure. http://t.co/WDY2ifCoBi
— Shashank Joshi (@shashj) February 26, 2015So Emwazi hangs around with an al-Shabab terrorist. Then is "incensed" when he's not allowed to go to Kuwait. Right. http://t.co/bjlHFDFFUS
— Shashank Joshi (@shashj) February 26, 2015Mohammed Emwazi as Rorschach test: Did the state radicalize him? Or did the state correctly ID a radical? http://t.co/G0zu9PkjKK
— Andrew Exum (@ExumAM) February 26, 2015Just as I suspected, people are already rolling out their Jump To Conclusions Mats regarding the motives and radicalization of Emwazi.
— Andrew Exum (@ExumAM) February 26, 2015The Guardian almost makes UK man behind ISIS beheadings into a victim of persecution | http://t.co/RYakh72R0A
— Mike Doran (@Doranimated) February 26, 2015Going to safari in Tanzania. Like that chap who went to a wedding in Afghanistan and had such a good time he didn't come back.
— Michael Weiss (@michaeldweiss) February 26, 2015Yaroslav Trofimov wrote in The Wall Street Journal earlier this year that the "Islamic State’s ability to lure thousands of Westerners is unprecedented in modern history."
Trofimov explained that many of these "newly baked jihadists" are frustrated with their own countries and have "embraced Islamic State’s genocidal cult simply because it is the most obvious counterpoint to the West."
Thomas Hegghammer, director of terrorism research at the Norwegian Defense Research Establishment, told The Journal: "It is fundamentally the same malaise that is also inspiring the far-left activists. A lot of young people have the same idea that the capitalism-centric Western system is not for them, and that another society is being set up."
ISIS, which has claimed large swaths of Iraq and Syria, is trying to build an Islamic state ostensibly governed by a 7th-century interpretation of sharia law.
Thousands of Westerners are thought to have traveled to the Middle East to join Islamist groups.
Michael B. Kelley contributed to an earlier version of this report.
SEE ALSO: ISIS defector describes how 'Jihadi John' ran executions
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