Terrorist Usman Khan begged to be allowed to take part in a deradicalisation course after his conviction for terror offences - saying he wanted to be a "good British citizen".
A handwritten note from the killer, who was gunned down by police yesterday after he fatally stabbed two people and injured three more, has emerged.
Khan, 28, was jailed in 2012 and automatically released in December last year without appearing before a parole board.
In the months after his conviction, while serving his sentence in HMP Belmarsh, Khan said he had been "immature" and said he no longer held extremist views.
The letter, published by ITV News , states: "I would be grateful if you could arrange some kind of course that I can do where I can properly learn Islam and its teachings, and I can prove I don't carry the extreme views which I might have carried before."
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And it continues: “I would like to do such a course so I can prove to the authorities, my family and soicity (sic) in general that I don’t carry the views I had before my arrest and also I can prove that at the time I was immature, and now I am much more mature and want to live my life as a good Muslim and also a good citizen of Britain.”
Khan's lawyer Vajahat Sharif told The Guardian that although his client wanted to deradicalise, no support was available.
It is possible he was "regroomed" after his release, Mr Sharif said.
The lawyer stated: “He requested intervention by a deradicaliser when he was in prison.
“The only option was the probation service and they cannot deal with these offenders."
He added that the probation service "cannot deal" with ideological criminals.
Mr Sharif said he last spoke with Khan in March after he was released on the condition that he lived in a bail hostel and reported to a police station every day.
He said Khan had been a "model prisoner" at HMP Whitemoor, and said he believed he had reformed.
The lawyer stated: "Maybe he was not ideologically robust enough to resist the radicalising groomers – I thought he was a reformed character."
Experts claim Khan may have been seeking revenge for the death of ISIS leader Abu Bakr al-Baghdadi.
Colonel Richard Kemp, ex-COBRA security committee chief, said: “If he turns out to be an Islamic terrorist, he was likely inspired by Islamic State.
“It is even possible his action was in revenge for al-Baghdadi's death. It’s something ISIS has called for since the US Delta Force raid in Syria."
Khan was automatically freed from prison a year ago and wearing an electronic monitoring tag.
Inspired by al-Qaida, he and others had plotted to bomb the London Stock Exchange and target other sites including the Houses of Parliament and the US Embassy, as well as then-mayor Boris Johnson , the Dean of St Paul's Cathedral and two rabbis.
He was charged in December 2010 and convicted in February 2012 of terrorism offences, but was released from prison last December on licence.
The Henry Jackson Society, a government think tank, found the number of terrorists or suspected terrorists who have been put on the government’s intensive “detoxification” scheme has almost tripled in a year.
Just 30 individuals attended DDP in 2016-17, its first year of operation - compare to 86 in 2017-18.
Dr Rakib Ehsan a research fellow at the Henry Jackson Society, said: "This attack will cast further doubt over the effectiveness of "deradicalisation schemes” including the Home Office's Desistance and Disengagement programme.
"As an acolyte of Islamist hate preacher Anjem Choudary, Usman Khan was a hardened fundamentalist who remained a major threat to society after his release.
"Simply relying on ‘deradicalisation’ courses - however well-meaning - is insufficient.
"These individuals are devious and are often capable of faking progress in order to fool those tasked with deradicalising them - with potentially deadly consequences."
