The man believed to have carried out the Streatham attack was a convicted terrorist fascinated with dying a martyr - who even once urged his girlfriend to kill her 'disbeliever' parents.
Then aged 18, Sudesh Amman had smiled and waved at the public gallery as he was jailed for three years and four months at the Old Bailey in December 2018.
The supporter of so-called Islamic State (IS) had pleaded guilty to possessing and distributing terrorist documents.
Amman is believed to have been back on the streets for just days before Sunday's stabbing attack - fulfilling one of his so-called life goals of dying a martyr.
His stash of manuals on bomb-making, knife-fighting and close combat included the titles 'Bloody Brazilian Knife Fighting' and 'How To Make A Bomb In Your Kitchen'.
Police found a notepad in the North West London College student's home, in which the phrase "life goals" had been scrawled.
"Top of the list, above family activities, was dying a martyr and going to 'Jannah' - the afterlife," Alexis Boon, then head of the Metropolitan Police Counter Terrorism Command, said after he was jailed.
He said Amman had a "fierce interest in violence and martyrdom" and that he was fascinated with dying "in the name of terrorism", and added that the case was "a reminder of the need to be vigilant to signs of radicalisation and report it".
Amman, who had then lived with his family in Harrow, north-west London, posted al-Qaida propaganda on a family WhatsApp group, exposing siblings as young as 11 to graphic material.
He had also shared bomb-making literature via Skype chat and told his girlfriend of his wish to carry out acid attacks and that he preferred the idea of a knife attack over using bombs.
He also urged her to behead her 'disbeliever' parents in online chats.
Neighbours in Harrow told of their shock at what happened on Sunday.
Mechanical engineering apprentice Jignesh Khomani, 20, said he was "saddened" by the attack, and described Amman as "a pretty average guy".
He told the PA news agency: "There were no signs of anything (like this). He was just normal really.
"I just did not expect anything like this would happen. He did not seem like a character who would do something like that."
A teenager, who said she knew him from the local neighbourhood but did not want to give her name, said Amman used to talk about being a terrorist but she and others thought he was joking.
"He used to say 'I have got a grenade in my pocket, if you take one step closer to me I am going to set it off'," she said.
"We thought he was joking.
"He did used to say I am going to bomb you and I an going to be a terrorist but we were kids and thought he was joking but he kept on saying it."
Prosecutor Kelly Brocklehurst told the court at his sentencing that police were alerted by a Dutch blogger who identified extremist material in a Telegram chat in April 2018.
There was a photo of a knife and two firearms on a Shahada flag bearing Arabic words which mean "armed and ready".
An air gun, a black flag and a combat knife were seized from his home when he was arrested in May that year.
Mr Brocklehurst said: "The defendant had discussed with his family, friends and girlfriend his strong and often extreme views on jihad, the kuffar, and his desire to carry out a terrorist attack.
"Much of his fascination with conducting an attack was focused on using a knife but reference was also made to committing acid attacks on mopeds."
The prosecutor said Amman's interest in Islamic extremism and IS in particular was "more than a mere immature fascination with the taboo and with graphic violence".
He added: "He is clearly someone with sincerely held and concerning ideological beliefs."
Amman had entered guilty pleas to six charges of possession and seven of disseminating terrorism documents.
He denied three charges, which were ordered to lie on court file.
The science and maths student had previous convictions for possession of an offensive weapon and cannabis.
He was aged just 17 when he began collecting terrorist material in 2017.
Judge Mark Lucraft QC said Amman had a "very concerning series of offences".
