As early as September last year, MI5 and the FBI had identified
Emwazi as the masked killer – just a few weeks after US senators passed
legislation to authorise a $10m (£6.2m) reward for information that
would aid the arrest and conviction of the masked militant.
However security agencies did not make his name public mainly because
of fears about the impact his identification might have on hostages
being held by Islamic State. A secondary reason was concern over the
safety of Emwazi’s family in the UK, in case of retaliation.
According to people who have moved in jihadi circles in west London,
Emwazi began to be noticed about five or six years ago. “That’s when he
emerged, so to speak,” said one. "