Finsbury Park attacker Darren Osborne was radicalised in the space of just a few weeks after becoming obsessed with extreme far-right material online.
The 48-year-old was a “troubled, vile and hate-filled individual” who developed a “warped and twisted view” which drove him to murder, Dean Haydon, head of Scotland Yard’s counter terrorism command, said.
Osborne was set on a “path of radicalisation” after watching BBC drama Three Girls, based on the stories of victims of the Rochdale sex abuse scandal, in May last year.
The programme was the “first trigger” for his hatred towards the Muslim community, feelings which were further fuelled as he accessed extreme material online.
Mr Haydon said: “He has become, what I would call radicalised, within a period of three to four weeks in the lead-up to the attack.
“He certainly was not, as far as we can tell, interested in any extreme right-wing or domestic extremism groups or individuals up until that stage.”
He added: “It was clear that in the space of only a few weeks, Osborne had developed a warped and twisted view to such a degree that he was prepared to plan and carry out this attack.”
He had also set up a Twitter account and had followed and accessed tweets by Mr Robinson, Woolwich Crown Court heard.
Mr Haydon said: “He became obsessed then with that type of material and what we think is that then sent him into a further spiral of wishing to do an attack.”
Osborne came from a “dysfunctional” background and had a history of violence, having served two years in prison for assault, and had suffered from depression, alcohol and drug abuse.