The terrorist murders committed by Usman Khan have raised questions over the early release of certain prisoners and the impact of rehabilitation programmes.
The attacks on Friday prompted the Ministry of Justice to review the licence conditions of every convicted terrorist released from prison.
The Prime Minister Boris Johnson has claimed this applies to at least 74 people.
Why was Usman Khan released half way in to his sentence?
Usman Khan and two other men who planned to raise money to build a training camp for terrorists in Pakistan, were originally given indeterminate jail sentences for public protection.
Khan was given eight years behind bars, and would be assessed for release by the Parole Board after this sentence was completed. He would have been released on licence for at least 10 years if he was found to be safe.
If he was found to be dangerous, Khan would have remained in prison, potentially for the rest of his life.
But Khan and his co-defendants, Nazam Hussain and Abdul Bosher Mohammed Shahjahan, all from Stoke-on-Trent, successfully appealed against their sentences in 2013.
They claimed they had been unfairly classed as more dangerous than other members of their terror cell, who were plotting to bomb the London Stock Exchange.
Khan was given a fixed jail term of 16 years, with an extended licence period of five years, meaning he was automatically released after serving half his jail term, but would have remained on licence after release for 13 years.
If he broke the conditions of his release during this time, he could be sent back to prison.
Would the Tories' proposed changes to automatic release affect a case like Khan's?
The Conservatives say criminals sentenced to at least four years in prison for crimes which carry a maximum life term would no longer be released at the halfway point.
Those offenders will be required to serve two-thirds of their sentence behind bars.
But for Khan's case, the type of indeterminate sentence he received was scrapped in 2012, and the current equivalent is an extended determinate sentence.
Under that system, defendants given less than 10 years are already automatically released after serving two-thirds of their sentence, so the changes would not affect them.
What attempts were made to stop Khan re-offending?
Khan made the authorities think he had changed.
He wrote a remorseful letter to the Home Office in 2012, asking to partake in a deradicalisation programme, saying he was "immature" when he committed his offences.
He insisted that he wanted to be "a good citizen of Britain".
But it has also been reported that he refused to take part in the programmes while in high security jail Belmarsh.
On release, he would have taken part in the Government's Desistance and Disengagement Programme, that aims to stop offenders taking part in terrorist activity and move them away from radical ideologies.
Khan was 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.