British authorities came under pressure Friday to explain how they let the suspected militant who would come to represent the extreme brutality of the group Islamic State slip through their grasp.
Mohammed Emwazi, a 26-year-old, university-educated Londoner, had been on the radar of British intelligence officials since at least 2009, five years before he is believed to have appeared in videos as the masked executioner of American and British hostages.
Prime Minister David Cameron defended the country's security services, saying they are "incredibly impressive, hardworking, dedicated, courageous and effective at protecting our country."
"All of the time, they are having to make incredibly difficult judgments, and I think basically they make very good judgments on our behalf," Cameron told reporters during a visit to Cardiff, Wales.
However, security analysts said questions would need to be answered about how Emwazi was transformed from soccer-loving schoolboy to the menacing figure featured in the beheading videos, how he was able to travel to Syria around 2013, and whether the country's intelligence services have the resources they need to respond to homegrown extremism.
"They are paid to keep us safe, and if they don't keep us safe, I'm afraid to say they have failed," said Anthony Glees, director of the Center for Security and Intelligence Studies at the University of Buckingham. "That's not an argument for getting rid of them or reducing their activity, it's an argument for increasing their resources."
Britain's Daily Telegraph newspaper ran a front-page article Friday on the intelligence "blunders that allowed Jihadi John to slip the net."
"MI5 and Mohammed Emwazi: Agency must answer serious questions," said a headline on the Guardian's website.
There are conflicting accounts of how Emwazi became radicalized. A Muslim advocacy group called CAGE charged Thursday that harassment by the security services played a major role.
Emwazi complained to the group about being detained with two friends in Tanzania in 2009, repeatedly questioned, and prevented from moving to Kuwait, where he said he had a job and fiancee waiting.
Court documents obtained by the BBC suggested that Emwazi may already have been associating with suspected radicals at the time. The documents filed in 2011 allege that Emwazi was part of a group known as the North London Boys, which had been funneling equipment, funds and fighters to the Somali militant group Shabab.
Another man associated with the group, Bilal Berjawi, joined Shabab in Somalia and was killed in a 2012 drone strike, said Shashank Joshi, a researcher on international security at the Royal United Services Institute in London.
Berjawi told his family that he was traveling to Africa on safari, the same explanation later provided by Emwazi. Berjawi was detained in Kenya in February 2009 and sent back to Britain, but is believed to have made it to Somalia in October that year.
"In my mind, it's pretty clear the services were interested in these networks because of the threats they posed, and that they did not cause that radicalization," Joshi said. "They may have overstepped the line at times … but they faced an extraordinarily difficult dilemma of how you monitor these things within a law that was basically constraining."
Anti-terrorism legislation passed in 2005 gave British authorities sweeping powers to monitor suspects and place them under effective house arrest by issuing what were known as control orders. Under pressure from civil liberty campaigners, the system was abolished in 2011 and replaced with less restrictive measures.
"According to officials, that complicated their ability to disrupt these networks and increased the need to conduct the very resource-intensive surveillance," Joshi said.
Members of the North London Boys were reportedly adept at evading surveillance, holding meetings in public places where their communications couldn't be monitored.
There were also limits to the number of people who could be monitored, experts said. Hundreds of Britons are believed to have traveled to Syria to join militant groups in recent years.
"One of the difficulties here is you can't keep an eye on everyone all the time," former Liberal Democrat leader Menzies Campbell, who sits on Parliament's intelligence and security committee, said in a BBC radio interview.
In the case of Emwazi, an assessment was made that while he might wish to join a militant group, he did not have the ability to act on that desire, Glees said. "I think it's clearly self-evident they made the wrong call."
British authorities have not officially named Emwazi as the militant nicknamed "Jihadi John," who appeared in videos showing the killing of American journalists James Foley, Steven Sotloff and others. But his identity was confirmed Thursday by a Western official in Washington.
The widow of one of Emwazi's alleged victims, British aid worker David Haines, said she wanted to see him captured alive.
"If he gets killed in action … it would be an honorable death for him and that is actually the last thing I would want for someone like him," Dragana Haines told the BBC.
But David Haines' daughter, Bethany, told Britain's ITV News that she would only get closure when there is a "bullet between the eyes" of Emwazi.
More details emerged Friday about Emwazi, who was born in Kuwait, moved to Britain with his family at the age of 6 and reportedly dreamed of becoming a professional soccer player.
British newspapers published a picture of him at age 10, posing for a class photograph. In his school yearbook he said his favorite soccer club was Manchester United, his favorite color was blue and his favorite cartoon was "The Simpsons."
Asked where he thought he would be when he turned 30, he wrote in a childish scrawl: "I will be in a football team and scoring a goal."
Special correspondent Boyle reported from London and Times staff writer Zavis from Los Angeles.