The FBI director says the US believes it has identified the British-accented masked man in the videos depicting the beheadings of two American journalists and a British aid worker.
FBI Director James Comey told reporters at the bureau's headquarters Thursday he would not reveal the man's name or nationality.
Comey did not address whether the US believes the man actually carried out the killings himself. The full beheadings are not shown in the videos, but the British-accented, English-speaking militant holds a long knife and appears to begin cutting the three men: American reporters James Foley and Steven Sotloff and British aid worker David Haines.
In late August, British Ambassador Peter Westmacott said his country was close to identifying the Islamic State group militant.