LONDON — The world knows him as "Jihadi John," the masked, knife-wielding militant in videos showing Western hostages being beheaded by the Islamic State group. On Thursday, he was identified as a London-raised university graduate known to British intelligence for more than five years.
The British-accented militant from the chilling videos is Mohammed Emwazi, a man in his mid-20s who was born in Kuwait and raised in a modest, mixed-income area of west London.
No one answered the door at the brick row house where Emwazi's family is said to have lived. Neighbors in the area of public housing projects either declined comment or said they didn't know the family.
British anti-terror officials wouldn't confirm the man's identity, citing a "live counterterrorism investigation." But a well-placed Western official, speaking on condition of anonymity because he wasn't authorized to speak publicly, confirmed he is Emwazi.
One man who knew Emwazi portrayed him as compassionate, a description completely at odds with the cruelty attributed to him.
"The Mohammed that I knew was extremely kind, extremely gentle, extremely soft-spoken, was the most humble young person that I knew," said Asim Qureshi of CAGE, a London-based advocacy group that counsels Muslims in conflict with British intelligence services.
Qureshi noted strong similarities between the man in the beheading videos and Emwazi, who he first met in 2009. But, "I can't be 100 percent certain."
"The guy's got a hood on his head. It's very, very difficult," Qureshi said, adding that his last contact with Emwazi was in January 2012.
Asked whether it was helpful or hurtful to have the jihadi publicly identified, White House Press Secretary Josh Earnest said that investigators over the last several months "have found it to their advantage to not talk publicly about the details or progress of that investigation." He didn't confirm the identity of the suspect.
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.
"Jihadi John" appeared in a video released in August showing the slaying of American journalist James Foley, denouncing the West before the killing. Former captives identified him as one of a group of British militants that prisoners had nicknamed "The Beatles."
A man with similar stature and voice was 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.
The Washington Post and the BBC, which first identified the masked man in the video as Emwazi, said he 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 British authorities before he traveled to Syria in 2012, and Qureshi said Emwazi had accused British intelligence agents of harassing him.
Emwazi first contacted CAGE in 2009, Qureshi 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 the 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."
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.
Congregants leaving a mosque in the west London neighborhood where Emwazi is believed to have lived 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.
Maher said it appears that Emwazi survived, and has become one of the most prominent members of the Islamic State group, 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 said they felt "relieved" and "take comfort" after Emwazi's identity was revealed, and hope he will be caught and sent to prison.
"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 said, according to the BBC.
Associated Press writers Raphael Satter and Danica Kirka in London, and Eric Tucker and Nancy Benac in Washington contributed to this report.