The terrorist who murdered three people including a police officer was British-born and had been investigated by MI5 in the past, it was revealed yesterday.
Theresa May told the Commons that the fanatic, who mowed down tourists and workers with a car on Westminster Bridge on Wednesday, had been probed in relation to violent extremism.
The prime minister said his identity was known to police and the security services, saying: “The man was British-born and some years ago he was once investigated by MI5 in relation to concerns about violent extremism. He was a peripheral figure.”
She described the case as “historic”, saying the killer was not part of the “current intelligence picture” and adding: “There was no prior intelligence of his intent or of the plot.”
In a statement she praised the exceptional bravery of police officers, saying: “On Wednesday we saw the worst of humanity but we will remember the best.”
Her comments came after armed police stormed homes in London and Birmingham in a series of raids after the terror attack that brought carnage to the heart of Westminster.
Eight people were arrested in a fast-moving counter-terror operation after the worst atrocity in the UK since the 2005 London bombings.
Police yesterday said casualty figures were not as high as first feared, saying four people were confirmed dead — including police constable Keith Palmer, an officer guarding Westminster Palace, and the lone terrorist.
Two pedestrians were also killed as the attacker mowed down tourists and workers with a 4x4 Hyundai car on Westminster Bridge before crashing into railings in front of Parliament.
The maniac, clutching two knives, was shot dead by armed police after he burst through the gates to the Palace of Westminster, stabbing Palmer, one of several unarmed officers guarding the entrance. The policeman, 48, a father and husband, was killed as he and a colleague tried to stop the attacker at about 2.30pm.
The officer, a member of the Parliamentary and Diplomatic Protection Squad who had served for 15 years, died in the main courtyard just yards from the Commons after desperate attempts to save his life by paramedics and MPs, including Foreign Office minister Tobias Ellwood.
Yesterday assistant commissioner Mark Rowley, the head of UK counter- terrorism, said police believed the assailant acted alone and was inspired by international terrorism.
He revised the death toll down from five to four and said 29 people had been injured and taken to hospital, while an unknown number had been injured and were walking wounded.
The injured included three Met officers who were among those mown down on the bridge as they walked back from a commendation ceremony. Rowley said seven of the 29 are fighting for their lives in hospital in a critical condition.
Rowley said a “mix of nationalities” were among the dead and injured. He said: “Hundreds of detectives have been working through the night and in that time officers have searched six addresses and made seven arrests.
“The inquiries in Birmingham, London and other parts of the country are continuing.” 
The counter-terror operation is focusing on the background of the assailant, how he got hold of the car, where it has been in the past day or two and if he had associates who helped him.
At the scene of one police raid — a flat in Hagley Road, Birmingham — one witness said: “The man from London lived here.” Rowley said police believe the attacker worked alone, supporting a theory the assailant was a “lone wolf” fanatic inspired by the Islamic State.
Mayor Sadiq Khan said Londoners would go about their everyday lives as usual “because that’s who we are”.
Defence secretary Michael Fallon said security arrangements at Westminster would be reviewed. He added that extra patrols were being deployed across the capital, with some leave cancelled, but otherwise it was “business as usual in London”.



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