The release of the convicted terrorist behind Friday's London Bridge attack from Belmarsh prison in 2012 has raised questions over the early release of certain prisoners.

Usman Khan, the suspect shot dead after stabbing two people to death at a prisoner rehabilitation conference on Friday, had been released from Belmarsh prison out on licence after being convicted of terror offences.

His release and subsequent murders have raised questions over the early release of certain prisoners and the success of rehabilitation.

Usman Khan was ordered to spend at least eight years behind bars as part of a gang of nine extremists who were sentenced in February 2012 in Woolwich Crown Court over an Al-Qaeda inspired plot.

He and two other men planned to raise money to build a terrorist training camp in Pakistan and recruit Britons to attend it, and were originally given indeterminate jail sentences for public protection.

Khan was due to be assessed for release on licence after those eight years, with the possibility of remaining in prison for the rest of his life.

However in 2013 Khan and his co-defendants, Nazam Hussain and Abdul Bosher Mohammed Shahjahan, all from Stoke-on-Trent, successfully appealed against their sentences.

They argued that they had been unfairly classed as more dangerous than other members of their terror cell, who were plotting to bomb the London Stock Exchange.

So Khan was instead given a fixed jail term of 16 years, with an extended licence period of five years.

This meant he was automatically released from the high security jail, Belmarsh, after serving half his jail term, but would have remained on licence after release for 13 years.

Many have said Khan hoodwinked the authorities into thinking he had changed his ways, and it was at a Cambridge University conference on prisoner rehabilitation when witnesses said he "flipped" and launched his attack.

Jack Merritt, 25, and Saskia Jones, 23, were today commemorated at the services, after being stabbed to death by the convicted terrorist.

They were stabbed to death by convicted terrorist Usman Khan, 28, at a prisoner rehabilitation conference on Friday.

While in jail in 2012, Khan wrote an apparently contrite letter to the Home Office asking to take part in a deradicalisation programme, and claiming that he had been "immature" when he committed his offences.

However, it has also been reported that he refused to take part in deradicalisation programmes while in high security jail Belmarsh.

He was also wearing an electronic tag at the time of the attack, which is designed to enforce curfews, and reportedly would have had to report his plans to travel to London to police.

A political row has broken out between the political party leaders about the release of prisoners, and the leaders have also been accused of "politicising" the London Bridge attack.