Ten people have been arrested, vehicles were seized, and police are combing through massive amounts of computer data following a series of raids carried out in the aftermath of the deadly rampage outside Britain’s Parliament by a lone attacker in London on Wednesday.

Yesterday, authorities also identified the attacker responsible for the deaths of four people and the serious injury of scores of other as Khalid Masood, 52.

Khalid Masood

Masood was born Adrian Russell in Kent to the southeast of London in 1964. He adopted the name Khalid Masood when he converted to Islam later in life. Prior to that, he also used Ajao, the surname of his stepfather, and is also known by the name Adrian Elms.

Masood was known to be police as he was convicted a number of times between 1983 and 2003 for offences which include assault and possession of an offensive weapon.

On Wednesday, Masood ploughed rented car into crowds on Westminster Bridge. He then crashed the vehicle into a fence outside Parliament grounds before stabbing an unarmed policeman in the area. Masood was shot dead by police moments later.

An American man from Utah, a British retiree and British female school administrator were killed on the bridge. The slain police officer was identified as Keith Palmer. Yesterday, 75-year-old Leslie Rhodes from south London became the fourth fatality when he died in the hospital on Thursday.

Authorities said more than 50 people were wounded in the attack, 31 of them required hospital treatment.

The terrorist group ISIS, also called Daesh, has claimed responsibility for the attack.

Police authorities described Masood as a radicalized. However, U.K. Prime Minister Theresa May said while Masood was investigated “some years ago” by British intelligence “in relation to concerns of violent extremism” but was not picked up because he was only considered a “peripheral figure.”

As of today, British police have search more than 21 properties in London, Brighton, Wales, Manchester and the central English city of Birmingham in and contacted thousands of witnesses.

Mark Rowley, head of Scotland Yard’s counter-terrorism department, told journalists that 10 people are now in custody in connection with the attack.

He said that while police believe Masood acted alone, investigators are now determining if there were other persons that “encouraged, supported or directed him.”