London police has named Khalid Masood as the man believed to have carried out the terror attack in Westminster.
The 52-year-old, who was shot dead by police, had not been the subject of any current police investigations, but had a range of previous convictions.
Khalid Masood was believed to have been living in the West Midlands.
ISIS has said it was behind the attack, in which Officer Keith Palmer, Aysha Frade and American tourist Kurt Cochran were killed.
Five men and three women were arrested in London and Birmingham on suspicion of preparation of terrorist acts following March 22 attack.
Police says detectives are continuing to search a number of addresses, including one in Carmarthenshire, three in Birmingham and one in east London. Addresses in Brighton and south-east London have also been searched.
Khalid 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 Officer Keith Palmer before being shot dead.
Police said there had been no prior intelligence about Khalid Masood’s intention to carry out an attack.
However, he was known to the police and his previous convictions included causing grievous bodily harm, possession of offensive weapons and public order offences.
Khalid Masood’s first conviction was in November 1983 for criminal damage and his last in December 2003 for possession of a knife.
He had not been convicted of any terrorism offences.
Scotland Yard said Khalid Masood “is not at this early stage believed to be his birth name” and that research into his aliases was being carried out.
Car rental company Enterprise said the vehicle used in the attack had been rented from its Spring Hill depot in Birmingham.