Details are emerging on London Bridge killer Usman Khan, a convicted terrorist who was freed from prison on an electronic tag and apparently attending a prisoner rehabilitation event when he struck, killing two.

Khan was imprisoned for his part in a plot to bomb the London Stock Exchange and pubs in Stoke, as well as planning to establish a terrorist training camp in Pakistan, in 2012, and originally serving an indeterminate sentence for public protection (IPP) — meaning he could have been kept behind bars as long as the relevant authorities deemed him too dangerous to release.

However, Court of Appeal judges led by Lord Leveson quashed his IPP in 2013 and swapped it for a fixed term of 16 years, with eligibility for release on licence at the halfway point — as is standard in the British criminal justice system.

Parole Board statement on London Bridge attack on Friday 29 November 2019. https://t.co/BXpVtcoal8 pic.twitter.com/gNV5ACi6cd — The Parole Board (@Parole_Board) November 30, 2019

Mohammed Shahjahan and Nazam Hussain, who were convicted as part of the same radical Islamic terror cell as Khan, also had IPPs changed to fixed terms, while a fourth man, Mohibur Rahman, had his term reduced by six months.

IPPs were abolished by the Tories altogether and the European Court of Human Rights (ECtHR) ruled they were “arbitrary”.

It should be noted that the European Court of Human rights is technically not a European Union institution, like the separate European Court of Justice (ECJ), but past Lord Chancellors such as Lord Falconer believe EU member-states are effectively required to submit to the ECtHR’s jurisdiction as a condition of EU membership.

“This individual was known to authorities, having been convicted in 2012 for terrorism offences. He was released from prison in December 2018 on licence and clearly, a key line of enquiry now is to establish how he came to carry out this attack.” — Metropolitan Police (@metpoliceuk) November 30, 2019

Metropolitan Police Assistant Commissioner Neil Basu confirmed that Khan “was known to authorities, having been convicted in 2012 for terrorism offences [and] released from prison in December 2018 on licence”, and that “The circumstances, as we currently understand them, are that [he] attended an event earlier on Friday afternoon at Fishmonger’s Hall called ‘Learning Together’.”

Khan is believed to have begun his attack at the prisoner rehabilitation event “before he left the building and proceeded onto London Bridge, where he was detained and subsequently confronted and shot by armed officers.”

Assistant Commissioner Basu also confirmed that “Tragically, two people – a man and a woman – were killed during the attack. Three others – a man and two women – were also injured and remain in hospital.”

The Metropolitan Police are appealing for “anyone with information, images or footage of the incident” to share it with them “on the UK Police Image appeal website https://ukpoliceimageappeal.co.uk/ … [or] call police, in confidence on 0800 789 321.”

"The public should continue to remain vigilant and report any concerns they have to police. If you see something that doesn’t seem right, trust your instincts and ACT by reporting to police, in confidence, at https://t.co/jdc8xdZ6iL.” — Metropolitan Police (@metpoliceuk) November 30, 2019

Follow Jack Montgomery on Twitter: @JackBMontgomery