Khalid Masood also injured dozens when he mowed down pedestrians in Westminster before stabbing a policeman to death outside Parliament on Wednesday.
The 52-year-old Muslim convert was born in Dartford, Kent but recently moved to Birmingham. He had also worked as an English teacher.
Neighbour Kaodi Campbell lived next door to the killer, and although she said she did not know him on a first-name basis, he was always “willing to help” jump-start her car.
Kaodi Campbell said she was shocked to hear the news of her neighbour
He helped me jump-start my car a few times
Speaking to ITV News in Birmingham, the 25-year-old said: “He was a [nice guy] to me, so I’m shocked from what I know of him.
“He helped me jump-start my car a few times, I spoke to his wife, she’d say ‘yeah, one sec’ I’ll get my husband’, he’d take his kids to school, just normal family living really.”
The Met Police said Masood, previously known as Adrian Russell Ajao, had used a number of aliases and had been known to police.
Armed with a knife, he stabbed PC Keith Palmer to death, before officers shot him dead in the devastating attack in the capital.
His previous convictions were violent and included possession of offensive weapons and public order offences.
The 25-year-old said Khalid Masood had helped her jump-start her car previously
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Police are now appealing for information to track down any “associates” of Masood.
Detectives say they have made two more “significant arrests” in their investigation, taking the total number to 10.
Speaking on Friday, Assistant Deputy Commissioner Mark Rowley said their investigation would focus on Mason’s “motivation, preparation and his associates".
London mourns terror attack at vigil Fri, March 24, 2017
The world grieves after an attacker killed three people and injured about 40 near parliament in London.
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Floral tributes are left after the vigil in Trafalgar Square, London to remember those who lost their lives in the Westminster terrorist attack
He said officers were trying to establish whether the killer "acted totally alone inspired by terrorist propaganda, or if others have encouraged, supported or directed him".
Mr Rowley added: "There might be people out there who did have concerns about Masood but did not feel comfortable for whatever reason in passing those concerns to us."
In total, 50 people were injured, 31 hospitalised with two in a critical condition and one receiving treatment for life-threatening injuries.
The Met says two police officers remained in hospital with "very significant" injuries.