The Westminster attacker was British-born and known to the police and intelligence services, the prime minister has revealed.
In a statement to the Commons, Theresa May said he had been investigated some years ago over violent extremism but had been a “peripheral figure”.
“A terrorist came, to the place where people of all nationalities and cultures gather to celebrate what it means to be free, and he took out his rage indiscriminately against innocent men, women and children,” Ms May said.
“He was not part of the current intelligence picture,” she said.
Eight arrests have been made following the attack on Wednesday that left four dead.
Those that died are PC Keith Palmer, Aysha Frade who worked at a London college, a man in his 50s and the attacker.
Seven of the injured are still in hospital in a critical condition.
A further 29 had been treated in hospital, Mr Rowley added.
In the attack on Wednesday afternoon, a man drove a car along a pavement on Westminster Bridge knocking down pedestrians, creating panic and leaving dozens injured.
He then ran towards Parliament where he stabbed PC Palmer who was unarmed. Armed police then shot dead the attacker in the grounds.
“This was an attack on free people everywhere”.