London - Experts say police and security services are using voice-recognition software and other technology, as well as human tips, as they scramble to identify the militant recorded on a video showing the killing of American journalist James Foley.
Prime Minister David Cameron has said the masked jihadi is likely British. Linguists say his accent suggests he is from the London area.
The Guardian newspaper quoted an unnamed former captive who was held in Raqqa, Syria, as saying he appeared to be one of several British militants - nicknamed "The Beatles" by hostages - charged with guarding Islamic State prisoners.
John O'Regan, a linguist at London's Institute of Education, said on Thursday that analysts would likely make a voice print of the speaker and compare it to recordings of known suspects.