The Guardian reported Wednesday that, according to a former hostage, the British national who acted as executioner in the Foley murder video was one of three U.K. citizens known among jihadists as the "Beatles," who are in charge of holding foreign hostages in the Syrian city of Raqqa.
Shiraz Maher, a senior research fellow at the Center for the Study of Radicalization at King's College London, said he estimates that between 500 and 600 British citizens have gone to fight the Jihad in Syria, with the vast majority of these volunteers joining ISIS. He said that in his field research on the Turkish/Syrian border, rebel fighters have said the British foreign fighters are often the most extreme.