The horrifying video of James Foley’s execution is dominated by three colors. The orange of Foley’s tunic. The taupe of the desert. And the black of an Islamic State militant’s uniform — a uniform worn by a man speaking with what experts think is a British accent. In the span of two days, the masked man has become perhaps the world’s most notorious terrorist.

But despite the infamy, he remains enigmatic. Where did he come from? How old is he? What drove him to such extremism?

Answers to those questions are unclear. But the militant now has an identity. As per the British press, the masked man is known as “Jihadi John.” The nickname speaks to claims slowly trickling out about the killer.

John’s accent, which experts contend signifies London origins, is the source of his alias, the BBC reported in a radio broadcast on Thursday. John is believed to lead a small  cadre of three British militants who guard the Islamic State’s foreign hostages. Because of their captors’ accents, hostages called them “John, Paul and Ringo after the Beatles,” the BBC’s Frank Gardner reported on Thursday.

It’s not surprising that Foley’s executioner was a foreigner — specifically, a Briton. Militants from Britain account for a larger proportion of the Islamic State’s forces than nearly every other Western country. Estimates place their number anywhere from 800 to 1,500. Today, more British Muslims may fight for the Islamic State than for Britain’s own military, according to USA Today and the Times of London, underscoring the militants’ presence in the United Kingdom. Recruiters recently passed out Islamic State propaganda in London advocating enlistment, and supporters flew a black jihadist flag there earlier this month.

Such fighters are more radicalized than other members of the Islamic State. “Foreign fighters are often used for the most brutal acts because they are the most ideologically motivated,” Peter Neumann, director of the International Center for the Study of Radicalization, told The Washington Post’s Griff Witte. “The locals may say, ‘That’s not the kind of thing we do here.’ But the outsiders don’t know that.”

Of particular brutality was James Foley’s executioner. John is an “intelligent, educated and a devout believer in radical Islamic teachings,” according to the Guardian, which interviewed a hostage who was also held captive by him. He is reported to have led negotiations with at least eight Western families in the past year for the release of their loved ones, and may have been involved last spring when Islamic State militants released two Spanish journalists.

But the Islamic State’s correspondence with Foley’s family was different. The group demanded the astronomical sum of $132 million for his release, a “number so absurdly high that private third parties or insurance groups that cover kidnappings would have struggled to pay it,” wrote The Post’s Adam Taylor. It was so high, in fact, that most experts agree the Islamic State never expected to get paid. Foley, it seemed, would be reserved for something else.

John and the rest of the guards disliked Foley. They seized his laptop, and their subsequent discovery that Foley’s brother served in the U.S. Air Force stirred acts of recrimination, fellow hostage Didier Francois told Europe 1 Radio. “Being an American, he was probably more targeted by the kidnappers,” another captured French journalist told the BBC. “Well, he would be beaten a bit more probably, he was some kind of scapegoat. And the kidnappers knew that his brother was in the U.S. Air Force. He became the whipping-boy of the jailers.”

One particularly brutal scene came right before Francois’s release in April of this year. The jihadists began to perform mock executions on Foley. “One of the last times I saw him before leaving, the group — which has macabre taste — had forced him to pose as if he was being crucified against a wall,” François said, according to the Wall Street Journal..

Finally, on Aug. 12, days before Foley’s execution, his captors sent a final e-mail to Foley’s family. The publication Foley wrote for, GlobalPost, published the letter in full with the permission of Folely’s family.

“HOW LONG WILL THE SHEEP FOLLOW THE BLIND SHEPPARD?” it read. “…As for the scum of your society who are held by us, THEY DARED TO ENTER THE LION’S DEN AND WHERE EATEN! … Today our swords are unsheathed towards you, GOVERNMENT AND CITIZENS ALIKE! AND WE WILL NOT STOP UNTILL WE QUENCH OUR THIRST FOR YOUR BLOOD. … You and your citizens will pay the price of your bombings! The first of which being the blood of the American citizen, James Foley! He will be executed as a DIRECT result of your transgressions toward us!”