LONDON (AFP) - Khalid Masood, the Briton behind this week's terror attack on parliament, was a Muslim convert with a history of violence who was known to security services but only as a "peripheral" figure.
Police said the 52-year-old father, who also used the names Adrian Elms and Adrian Russell Ajao, was not under investigation when he went on the rampage in Westminster on Wednesday, killing four people.
They believe he was acting alone, but described the attack as "Islamist-inspired", while the Islamic State group claimed he was one of their "soldiers".
Masood was born on Christmas Day 1964 to a single mother, who remarried when he was young and brought him and his step-brothers up in a middle-class area of Kent, in southeast England, according to media reports.
Former schoolmates said he had been a popular student who excelled academically and at sport, and that he was a "happy-go-lucky" character.
His first brush with the law came in 1983, with a conviction for criminal damage, while further convictions for assault and possession of offensive weapons would follow over the next 20 years.
Mark Ashdown, an old schoolfriend, described "Ade" as he knew him as a "Jack-the-lad" character with whom he used to go out partying, drinking, taking drugs and chasing girls.
But he said he was changed by a fight in his local village pub in Sussex, southern England, after which Masood was jailed in 2000 for slashing a man's face.
"When he first came out he told me he'd become a Muslim in prison, and I thought he was joking," Ashdown told The Sun.
"Then I saw he was quieter and much more serious. I gave him some cash-in-hand work for a few months as a labourer."
Another man who witnessed the pub attack, Lee Lawrence, told the tabloid that Masood told him, "I just want blood, I dream about killing someone."
He soon got into trouble again. Police said his last conviction was in 2003, for the possession of a knife, in what reports said was another violent attack on a man.
Prime Minister Theresa May said Masood was once investigated by British domestic spy agency MI5 in relation to "concerns about violent extremism", but was not part of the current "intelligence picture".
Masood spent time as an English teacher in Saudi Arabia, including year-long stints starting in November 2005 and again in April 2008, and returned for the Hajj in 2015.
But the Saudi embassy in London said in a statement, "During his time in Saudi Arabia, Khalid Masood did not appear on the security services' radar and does not have a criminal record in the Kingdom of Saudi Arabia."
The Islamic State group claimed that one of its "soldiers" had carried out the London attack following a call to target countries fighting the jihadists in Iraq and Syria.
Police said they were seeking to establish if Masood was inspired by terrorist propaganda, or if "others have encouraged, supported or directed him".
Laughing and joking
Masood lived in several locations around southern England over the years, fathering two daughters with his first wife, before having a short-lived marriage with a Muslim woman, according to media reports.
At the time of the attack, he was believed to have been living in the central English city of Birmingham, reportedly with another partner and one or more young children.
The night before, Masood stayed in a hotel in Brighton on the southern English coast, where he told staff he was visiting friends.
He had rented a car that he later used to mow down pedestrians on Westminster Bridge from a branch of Enterprise in Solihull in Birmingham, the company confirmed.
Sabeur Toumi, manager of the Preston Park Hotel in Brighton, told Sky News that police had shown him a photo to confirm Masood's identity.
The attacker, who had also stayed the previous Friday, had been "very friendly, laughing and joking", and discussed his family in Birmingham, he said.
"It is very shocking because these days you don't know who are the bad ones and who are the good ones. He was just like any other guest who checked into the hotel."
"He was a nice guy. I used to see him outside doing his garden," Iwona Romek, a former neighbour, told the Birmingham Mail.
Romek said the family had abruptly moved out of their house in Winson Green, a neighbourhood in western Birmingham, around Christmas without saying goodbye.
More recently Masood may have been living in a flat next to a Persian restaurant and a pizza parlour in the upmarket Edgbaston neighbourhood, according to reports.