"A masked, black-clad militant, who has been identified by the Washington Post newspaper as a Briton named Mohammed Emwazi, brandishes a knife in this still image from a 2014 video obtained from SITE Intel Group February 26, 2015. Investigators believe that the masked killer known as ""Jihadi John"", who fronted Islamic State beheading videos, is Emwazi, two U.S. government sources said on Thursday. The British government and police refused to confirm or deny his identity, which was first revealed by the Washington Post, saying it was an ongoing security investigation. REUTERS/SITE Intel Group/Handout via Reuters (CIVIL UNREST POLITICS CRIME LAW CONFLICT) ATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THE AUTHENTICITY, CONTENT, LOCATION OR DATE OF THIS IMAGE. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS PICTURE WAS PROCESSED BY REUTERS TO ENHANCE QUALITY. AN UNPROCESSED VERSION WILL BE PROVIDED SEPARATELY"
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