MI5 and Mohammed Emwazi: The history of 'Jihadi John'

It has emerged that the intelligence services tracked the movements of a London man they suspected was trying to travel to Somalia to join Islamist extremists.

However Mohammed Emwazi did manage to leave the UK in 2013, and reach Syria.

The BBC's Frank Gardner considers how Emwazi became radicalised, and how he was handled by British security services.