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Manu Brabo, AP
FILE - This September 2012 file photo posted on the website freejamesfoley.org shows journalist James Foley in Aleppo, Syria.In a horrifying act of revenge for U.S. airstrikes in northern Iraq, militants with the Islamic State extremist group have beheaded Foley — and are threatening to kill another hostage, U.S. officials say. (AP Photo/freejamesfoley.org, Manu Brabo, File) NO SALES

The British ambassador to the United States said Sunday that investigators were close to identifying the young militant with a British accent who beheaded American journalist James W. Foley on a video released last week by the Islamic State.

The ambassador, Peter Westmacott, said in an interview on CNN that British counterterrorism officers, supported by American counterparts, were making progress in using clues in the video to pick the killer out of the hundreds of British Muslims who had joined the Islamic State group.

“I do know from my colleagues at home that we are close,” he said. “But forgive me if I can’t go much further than that at this point.”

The ambassador said investigators were using voice-recognition technology to match the killer’s voice against recordings of known British militants now in Syria and Iraq. “We’re putting out a great deal of resource into identifying this person,” he said. “And there are some very sophisticated technologies, voice identification and so on, which people can use to check who these people are.”

If Foley’s killer is identified, it might give intelligence officials insight into the Islamic State kidnapping cell still holding another American reporter, Steven Sotloff, and other hostages, and could lead to criminal charges.

But with extremists in control of large parts of Syria and Iraq, it would be hard even to locate the suspect and highly risky to try to take him into custody anytime soon. An attempt early this summer by American Delta Force commandoes to rescue Foley and others held in Syria failed because the hostages had been moved.

“If things stay the way they are now, it would be difficult” to kill or capture the suspect, said a senior U.S. law enforcement official, who spoke on the condition of anonymity because of the continuing investigation. The official said that the FBI and CIA, working with their British counterparts, MI-5 and MI-6, had narrowed to “a short list” the suspects in Foley’s execution.

The five-minute video released by Islamic State, now the focus of intensive forensic analysis by British and American authorities, is narrated in part by the hooded killer. From an analysis of the video images, investigators could estimate the man’s height, study details of his eyes and eyebrows, and note his evident left-handedness. His voice likely has been matched against recordings of many of the 500 militant Britons estimated to have joined the Islamic State group.