The masked "Jihadi John" killer who fronted Islamic State beheading videos has been identified as Mohammed Emwazi, a British computer programming graduate from a well-to-do London family who was known to the security services. The black-clad militant brandishing a knife and speaking with an English accent was shown in videos released by Islamic State (IS) apparently decapitating hostages including Americans, Britons and Syrians. The 26-year-old militant used the videos to threaten the West, admonish its Arab allies and taunt President Barack Obama and British Prime Minister David Cameron before petrified hostages cowering in orange jump suits. Emwazi's name was first disclosed by the Washington Post. Two U.S. government sources who spoke on condition of anonymity confirmed to Reuters that investigators believed Jihadi John was Emwazi. Dressed entirely in black, a balaclava covering all but his eyes and the bridge of his nose and a holster under his left arm, Jihadi John became a menacing symbol of Islamic State brutality and one of the world's most wanted men. Hostages called him John as he and other Britons in Islamic State had been nicknamed the Beatles. He was unmasked publicly for the first time on Friday by British media which published a photograph showing Emwazi as a schoolboy. The Daily Mail newspaper published a picture showing Emwazi smiling and sitting cross-legged on the grass at the front of the photograph from the St Mary Magdalene Church of England primary school in Maida Vale, West London. Emwazi was born in Kuwait but came to Britain aged 6 and graduated with a computer programming degree from the University of Westminster before coming to the attention of Britain's main domestic intelligence service, MI5, according to an account given by Asim Qureshi, the research director of the Cage charity that campaigns for those detained on terrorism charges. Emwazi, a fluent Arabic speaker, said MI5 had tried to recruit him and then prevented him from traveling abroad, forcing him to flee abroad without telling his family, Qureshi told a news conference in London. Emwazi traveled to Syria around 2012, Qureshi said. MI5 does not publicly comment on the identity of militants or their backgrounds while an investigation is still ongoing. The British government and police declined to confirm or deny Emwazi's identity, citing an ongoing security investigation.