Why was the London Bridge attacker released?

The family of London Bridge attacker Usman Khan have said they are "saddened and shocked" by what happened and "totally condemn his actions".

Khan, who was convicted of a terrorism offence in 2012, killed Jack Merritt, 25, and Saskia Jones, 23, at a prisoner rehabilitation event on Friday.

The BBC's legal correspondent Clive Coleman looks at why he was released from prison on licence in December 2018.