LONDON (AP) — The world knows him as "Jihadi John," the masked, knife-wielding militant in videos showing Western hostages being beheaded by the Islamic State group. A growing body of evidence suggests he is a London-raised university graduate, described by one man who knew him as kind, gentle and humble.
The Washington Post and the BBC on Thursday identified the British-accented militant from the chilling videos as Mohammed Emwazi, a man in his mid-20s who was born in Kuwait and raised in a modest, mixed-income area of West London.
The Center for the Study of Radicalization and Political Violence at King's College London, which closely tracks fighters in Syria, said it believed the identification was correct.
Asim Qureshi of CAGE, a London-based advocacy group which works with Muslims in conflict with British intelligence services, said he saw strong similarities between the man in the video and Emwazi, whom he knew from 2009 to 2012.
But he said "I can't be 100 percent certain."
"The guy's got a hood on his head. It's very, very difficult," Qureshi said.
British anti-terror officials wouldn't confirm the man's identity, citing a "live counterterrorism investigation." National Security Council spokeswoman Bernadette Meehan said the U.S. couldn't confirm or deny the identity, either.
"Jihadi John" appeared in a video released in August showing the slaying of American journalist James Foley, denouncing the West before the killing. Former IS captives identified him as one of a group of British militants that prisoners had nicknamed "The Beatles."
A man with similar stature and voice also featured in videos of the killings of American journalist Steven Sotloff, Britons David Haines and Alan Hemming and U.S. aid worker Abdul-Rahman Kassig.
According to The Washington Post and the BBC, Emwazi was born in Kuwait, grew up in west London and studied computer programming at the University of Westminster. The university confirmed that a student of that name graduated in 2009.
"If these allegations are true, we are shocked and sickened by the news," the university said in a statement.
The news outlets said Emwazi was known to Britain's intelligence services before he traveled to Syria in 2012, and Qureshi said he had accused British spies of harassing him.
Qureshi said Emwazi first contacted CAGE in 2009. Emwazi said he had traveled to Tanzania with two other men after leaving university, but was deported and questioned in Amsterdam by British and Dutch intelligence services, who suspected him of attempting to join al-Shabaab militants in Somalia.
The following year, Emwazi accused British intelligence services of preventing him from traveling to Kuwait, where he planned to work and marry.
CAGE quoted an email Emwazi had sent saying, "I had a job waiting for me and marriage to get started. But now I feel like a prisoner, only not in a cage, in London."
"The Mohammed that I knew was extremely kind, extremely gentle, extremely soft-spoken, was the most humble young person that I knew," Qureshi said.
He said he hadn't had contact with Emwazi since January 2012.
Qureshi accused British authorities of alienating and radicalizing young British Muslims with heavy-handed policies.
"When we treat people as if they are outsiders, they will inevitably feel like outsiders, and they will look for belonging elsewhere," he said.
No one answered the door at the brick row house in west London where the Emwazi family is alleged to have lived. Neighbors in the surrounding area of public housing projects either declined comment or said they didn't know the family.
Congregants leaving a local mosque after afternoon prayers said they didn't know Emwazi and didn't believe he had worshipped there.
Neighbor Janine Kintenda, 47, who said she'd lived in the area for 16 years, was shocked at the news.
"Oh my God," she said, lifting her hand to her mouth. "This is bad. This is bad."
Shiraz Maher of the King's College radicalization center said he was investigating whether Emwazi was among a group of young West Londoners who traveled to Syria in about 2012.
Many of them are now dead, including Mohammad el-Araj, Ibrahim al-Mazwagi and Choukri Ellekhlifi, all killed in 2013.
Emwazi survived, and has become one of the most prominent members of IS, a fighter whose confidence and Western accent are calculated to strike fear into viewers of the group's grisly videos.
Maher said Emwazi's background was similar to that of other British jihadis, and disproved the idea "that these guys are all impoverished, that they're coming from deprived backgrounds."
"They are by and large upwardly mobile people, well educated," he said.
The daughter of British aid worker Haines, who was killed in September, told ITV News that identifying the masked man was "a good step."
"But I think all the families will feel closure and relief once there's a bullet between his eyes," Bethany Haines said.
Sotloff's family hopes his killer will be caught and go to prison, saying they felt "relieved" and "take comfort" after Emwazi's identity was revealed, according to the BBC.
"We want to sit in a courtroom, watch him sentenced and see him sent to a super-max prison where he will spend the rest of his life in isolation," the family added, according to the BBC.
Associated Press writers Raphael Satter and Danica Kirka contributed to this report.
Copyright 2015 The Associated Press.