The Dunstable mum of terrorist Sudesh Amman has told national media he was radicalised in prison.
Amman, 21, was judged "high risk" but still released from HMP Belmarsh after being convicted of terror offences at the Old Bailey in December 2018.
Yesterday, he was shot dead by armed police after stabbing two people in Streatham at around 2pm.
Haleema Faraz Khan, who lives in Dunstable, said she had visited her son at a bail hostel on Thursday and he called her hours before the attack.
She told MailOnline today: "He wasn't even a very devoted Muslim. He got radicalised while he was in Belmarsh Prison (in Thamesmead, South East London).
"He got into all this (supporting terrorism) on the internet, but when he went to prison something happened to him."
Mrs Khan is now trying to retrieve her son's body from police as soon as possible to bury him.
The government is considering emergency legislation in light of yesterday's terror attack.
The Muslim Council of Britain has condemned Amman's actions, saying it stands firm against hatred and division.
Harun Khan, the MCB secretary general, said: "Our thoughts are with the victims of the incident in Streatham, and our solidarity is with the people of that area. Streatham is a vibrant community where Muslims find common cause with fellow residents on a range of issues. Only recently, the people of Streatham came together to speak out against the vandalism against a local mosque.
"We must continue to celebrate this strong community spirit, whilst also remaining vigilant. We encourage everyone to report any hate crime and suspicious activity to the police to help keep our communities safe."