The United States says it believes it has identified the masked militant in the videos depicting the beheadings of two American journalists and a British aid worker.
FBI Director James Comey told reporters on September 25 that he won’t reveal the man's name or nationality.
In the three videos, the Islamic State (IS) militant speaks British-accented English before U.S. reporters James Foley and Steven Sotloff and British aid worker David Haines are decapitated.
Comey also said about a dozen Americans are believed to be currently fighting with Islamist groups in Syria.
He said more than 100 Americans have either tried to go to Syria and been arrested, gone successfully, or gone and come back.
The director said all the Americans who have returned after fighting with extremist groups are either under investigation, under surveillance, or have been arrested.
Based on reporting by AP and Reuters