LONDON — The Islamic militant in a video showing the death of American journalist James Foley took great care to disguise his identity, dressing head-to-toe in black, with a mask leaving only his eyes visible.

But police and intelligence services in Britain and the United States have a plethora of clues as they scramble to identify him, from image analysis and voice-recognition software to social media postings and testimony from former captives.

Prime Minister David Cameron has said the masked jihadi pictured holding a knife to Foley’s throat is likely British, and linguists say his accent suggests he is from the London area.

Britain’s Metropolitan Police is involved in the hunt for him, as are British intelligence agencies and the FBI.

The Guardian newspaper on Thursday quoted an unnamed former captive who was held by the Islamic State group in Raqqa, Syria, as saying he appeared to be one of several British militants – nicknamed “The Beatles” by hostages – charged with guarding prisoners.

BASIC AND HIGH-TECH DETECTIVE WORK

Peter Neumann, director of the International Center for the Study of Radicalization at King’s College London, said it was likely Foley’s beheading had taken place in Raqqa, a stronghold of the Islamic State militant group and the base for many of its foreign fighters.

He said investigators would use basic detective techniques to narrow down the field of suspects before turning to voice recognition software and other sophisticated technology.

Neumann said most of the hundreds of Western militants in Syria have Facebook or Twitter accounts, on which they post pictures of themselves and give away other clues to their origins, such as a favorite soccer team.

“Just because they are Islamic extremists and behead people doesn’t meant they don’t talk about football clubs,” he said.

Neumann said online photos could be analyzed to determine height, weight, eye color and other information.

LETTING THEIR GUARD DOWN ONLINE

He said that even though the militants, most in their teens and 20s, know they should be careful, they are so ingrained in online culture that “they let their guard down.”

Language experts say the masked killer sounds like a man in his 20s who was raised or educated in Britain. John O’Regan, a linguist at the University of London’s Institute of Education, said the militant spoke with a “multicultural London English” accent but with more formal standard English pronunciation, suggesting that his words had been carefully scripted.