The man believed to have carried out the attack in Westminster has been named by police as Khalid Masood.
Kent-born Masood, who died in the attack, was not the subject of any current police investigations, but had a range of previous convictions.
The 52-year-old was believed to have been living in the West Midlands.
The so-called Islamic State group has said it was behind the attack, in which PC Keith Palmer, Aysha Frade and US tourist Kurt Cochran were killed.
Eight arrests were made in London and Birmingham following Wednesday's attack.
Masood drove into pedestrians on Westminster Bridge before crashing his car into railings and then running into the grounds of Parliament, armed with a knife. He stabbed PC Palmer and then was shot dead.
Police said there had been no prior intelligence about his intention to carry out an attack.
But he was known to the police and his previous convictions included GBH, possession of offensive weapons and public order offences.
His first conviction was in November 1983 for criminal damage and his last conviction was in December 2003 for possession of a knife.
He had not been convicted of any terrorism offences.
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