A masked Islamic State militant seen wielding a knife in videos at the beheading of two Americans has been identified, FBI Director James Comey said on Thursday, but he declined to give the person's name or nationality.
The videos released in August and September of American journalists James Foley and Steven Sotloff showed a masked Islamic State militant brandishing a knife and speaking English with a British accent.
A European government source familiar with the investigation said that the accent indicated that the man was from London and likely from a community of Asian immigrants. U.S. and European officials said the principal investigative work identifying the man was conducted by British government agencies.
"I believe that we have identified," Comey told a small group of reporters. "I'm not going to tell you who I believe it is."
Actual beheadings were not shown on the Foley and Sotloff videos. The videos imply that the masked militant was the person who carried out the killings. But the videos did not show him actually drawing blood from the victims but faded to black after he finished his speeches and then cut to pictures of the beheaded bodies.
Investigators said that because of the way the videos were edited, it is possible that someone other than the British-accented man carried out the murders.
A third video purporting to depict the murder of David Haines, a British aid worker, surfaced later and Islamic State militants also have threatened to kill a second British aid worker, Alan Henning.
John Cantlie, a British journalist held by the group, has appeared in two Islamic State videos criticizing US airstrikes against the group and suggesting that the United States had become engaged in "Gulf War III."
The British ambassador to the United States, Sir Peter Westmacott, told CNN shortly after Foley's killing in August that Britain was working on identifying the suspect using voice-recognition technology. Westmacott said then that law enforcement was close to identifying the man.
British authorities had sought to keep a lid on news coverage of their investigation, hoping that might make it easier for authorities to capture militants implicated in the beheadings. Prime Minister David Cameron is scheduled to address the British parliament on Friday about his country's involvement in the fight against Islamic State.
FBI Director Comey told reporters about a dozen Americans were known to be fighting with militants in Syria, and some had already returned to the United States. Earlier, U.S. officials had said about 100 Americans had joined up.