http://www.cnn.com/2017/03/24/europe/london-attack/
Birmingham, England (CNN)Police investigating the deadly terrorist attack in central London are focusing closely on how the perpetrator became radicalized, as they battle to piece together his identity and connections.
Britain's most senior counter-terror police officer, Mark Rowley, described the inquiry as "very large and fast-paced," and announced two "significant arrests" Friday. Hundreds of officers had made contact with thousands of witnesses, he said.
Authorities had earlier portrayed the attacker, 52-year-old British man Khalid Masood, as having acted alone. It was unclear whether the arrests indicated that Masood may have had associates.
Masood is known to have used multiple aliases during his life. He was born Adrian Russell Ajao but also used the name Adrian Elms, police said.
Asked about his possible conversion to Islam and subsequent radicalization, Rowley said: "Clearly that's the main line of our investigation, is what led him to be radicalized, was it through influences in a community, influences from overseas, or through online propaganda."
He appealed for anyone who knew Masood well or was aware of his recent movements to get in touch, as detectives probe his motivation, his preparation for the attack and any associates.
Arrests and raids
Of 11 people arrested so far, two remained in custody as of late Friday, London's Metropolitan Police said. The two in custody are a 58-year-old man and a 27-year-old man, police said. Both men were arrested Thursday in Birmingham, according to police.
All but one of the people brought in were detained on suspicion of preparation of terrorist acts.
Arrests were made in London, Birmingham, central England, and Manchester, north west England, police said. Addresses were searched in Brighton, on the south coast of England, Surrey, to the west of London, and in the county of Carmarthenshire, in Wales. Two searches continue in Birmingham and one in London.
Officers have seized 2,700 items, including "massive amounts" of computer data, and have had contact with 3,500 witnesses to the attack, many of them of different nationalities, Rowley said.
The number of armed officers remains at nearly double strength in London in the wake of the attack, Rowley said, while extra police officers are also on patrol elsewhere in the UK.