He had a middle-class upbringing and lived with his attractive partner in a neat bungalow with a nameplate.
Khalid Masood's background in the heart of Middle England was as far removed from the stereotype image of an Islamic State 'soldier' as it is possible to imagine, the Daily Mail reports.
Security services are now investigating what drove a middle-aged English tutor from the Home Counties to unleash a Westminster atrocity - the worst terror attack on British soil since the July 7 bombings in 2005.
While IS recruitment propaganda typically shows disaffected young men posing with AK-47s and militaristic camouflage gear, Masood was 52 and a father-of-three when he decided to kill.
Even in the hours before the attack, witnesses said he was smiling and polite as he chatted about his plans to visit London, adding: "It isn't what it used to be."
Masood had lived briefly in the capital, but grew up in the affluent towns of Rye, East Sussex, and Tunbridge Wells in Kent, where friends recalled him as a popular, intelligent schoolboy who was obsessed with football and had no interest in religion.
He was born Adrian Russell Elms on Christmas Day, 1964, and his birth certificate gives his single mother's name as Janet Elms, a 17-year-old office worker from Croydon in South London.
His father's name is not recorded, although Miss Elms married Phillip Ajao two years later and he is listed as Masood's father in later records.
School friends at the Huntley School for Boys in Tunbridge Wells knew him as Adrian Ajao - or "black Ade" - and said he was popular and fun-loving.
Friend Kenton Till said: "He was very bright, very academic and he was very good at football.
"He wasn't religious at all. He was a big character, very friendly and a good laugh. He might have been the only black kid at the school. He experienced a little bit of racism but not a lot because he always tried to be popular."
Classmate Alan Keeble recalled a 'happy-go-lucky' character who excelled at sport and 'loved life', including reggae dance nights and a teenage flirtation with Mr Keeble's sister.
"He was in with everybody and everybody accepted him, because obviously a lot of us had never seen a black child before from Tunbridge Wells," he said. "I'm very shocked that he's done this."
Another friend, Tim Burchell, said Masood would sing soul music, "with a voice like Marvin Gaye".
"A whole load of us would go round to his house. He had a brilliant voice, a really good singer."
Despite his academic promise and popularity, Masood's life appeared to go off the rails soon after he left Huntley secondary school and began working at a local branch of Woolworths.
He was thrown out of a schoolmate's party after arriving with a drunken group of friends who had been smoking cannabis, and drifted away from his old school friends as he became involved with drugs.
A friend who asked not to be named said: 'In the early years he was all right - chirpy and cheeky and one of the lads. We used to go out drinking.
"As he got older he got a bit distant and lost his way, and I just put that down to drugs.
He got into drug dealing or taking drugs. He owed people a lot of money and then he just disappeared."
The friend said the teenage Masood had shown no interest in religion and had 'moaned' when his favourite pub had been turned into a mosque.
At 19 he received his first court conviction, for criminal damage in 1983, and he became increasingly involved in petty and violent crime.
Over the next two decades the burly bodybuilder was to be convicted of a catalogue of offences including assaults, grievous bodily harm, possession of weapons and public order offences, and was jailed twice.
He drifted from job to job, working as a sales rep and running a television aerial installation business. But in 1991 he met his his long-term partner Jane Harvey, 48, a successful businesswoman. He then moved into her £700,000 home in the well-to-do village of Northiam, near Rye in East Sussex.
The couple went on to have two daughters and Masood worked as a manager in Miss Harvey's business, Aaron Chemicals.
A friend, who did not want to be named, said Masood had been a 'charming' young man at the time when he met Miss Harvey.
Of Miss Harvey, known to her friends as Jay, she said: "Jay's a very efficient, business type person. She's always provided for her children."
But when their oldest daughter was eight, Masood was jailed for two years after slashing a man's face with a knife in a violent confrontation outside a local pub. He tried to blame racism for the appalling violence, which left his victim Piers Mott needing 20 stitches to a gaping wound in his cheek.
Masood told Hove Crown Court he snapped because of racism in the village and claimed he had been ostracised because villagers had a "view of black people".
Neighbours said he was radicalised during that two-year jail sentence, and abandoned his old life after his release from prison, including Miss Harvey and their two young daughters. One villager said: "When he got out of prison he decided he wanted to live an Islamic life and didn't want anything to do with his past life at all.
"He left Jay and the girls and went to live in some dump in Eastbourne, and I think he met someone else. He never came back after that and Jay was left to bring up the two girls on her own."
Tragedy struck when their elder daughter Andi was hit by a car as she ran to catch a school bus and was almost killed, the neighbour said. Her injuries were so serious that she was left in a wheelchair - a family tragedy which may have affected Masood's decision to use a car to mow down pedestrians on Westminster Bridge.
Masood convinced his elder daughter, now 24, to convert to Islam, change her name and wear a full face burka. It sparked a bitter fight with Miss Harvey. He had also asked his younger daughter, now 19, to convert and move to Birmingham with him, a friend added, but the girl refused. The friend said: "The elder daughter converted to Islam and is living in Birmingham.
"She wears a full face veil and I think had changed her name. It was her father who had helped convert her. He wanted the younger daughter to convert but Jane was against it and there was quite a family struggle. The couple's other daughter, now 19, lives with Miss Harvey and pictures show mother and daughter enjoying days out at the races or ice skating. There is no suggestion that any of the family, including the elder daughter, is a radical Islamist or knew about her father's extreme beliefs or his plans.
A casual acquaintance whop knew him when he moved to Eastbourne told the BBC Masood used both cocaine and bodybuilding steroids. But he was also on the cusp of a change in identity.
"I first met him in a pub around Christmas Eve 2001," the former electrician said. "I was introduced to him as "Black Ady".
'The next time I saw him it was summer 2002 - he was on steroids, though he wasn't huge. He took quite a lot of cocaine and he seemed to like women with pink hair . He had one girlfriend and she had silicone breasts.'
In 2004, Masood - still using the name Adrian Elms - married Farzana Malik, then a 25-year-old marketing assistant, at Medway Register Office in Rochester, Kent.
The couple have since split and she has married again.
Yesterday, Mrs Malik was being comforted by her family, including her second husband, at her home in Oldham.
On her Facebook page 'Soul Searchers', she describes Islamic fanaticism as "nonsensical", in a lengthy tirade which calls on her fellow Muslims to heed their true faith, concluding "unless they do that, radicalism will continue to plague the world."
Masood moved to Luton, when radical preacher Anjem Choudary was a frequent visitor to the town, and according to an online CV began working as an English tutor.
His next long term relationship was with Rohey Hydara, 39, with whom he shared a series of short-term homes in London and Luton.
Last night, the Met said Masood's partner Rohey Hydara, 39, was released on bail pending further inquiries. She was arrested on suspicion of preparing terrorist acts.
After his release from prison, he became estranged from his Christian mother Janet, now 69, who moved to rural Wales to build a new life away from her oldest son.
Mr and Mrs Ajao now live in a 200-year-old detached house in a remote area of Carmarthenshire where they rear chickens and pedigree sheep and Mrs Ajao sells hand-crafted cushions, handbags and blankets through her textile business, Folksy.
Their home was searched by police after the Westminster attack although police said the couple were not suspects and had not been arrested.
Neighbours said the pair were visited by their two sons Paul, 50, and Alexander, 40, but said they appeared to be estranged from Masood.
Mr Ajao is said to be seriously ill, and Masood told a hotel receptionist in Brighton he was dying from cancer, just hours before carrying out the Westminster attack.
Masood's siblings have gone on to very different careers.
Paul reportedly runs a florist's business in Banbury, Oxfordshire, and Alex is an account director at the Berlin office of an international marketing agency and has previously spoken of how he was briefly caught up in the 7/7 bombings, when he left London on a train from King's Cross just before the bombs exploded.
In his CV Masood described himself as British, "friendly and approachable" and a good listener, and claimed to have an economics degree.
He claims to have taught in Saudi Arabia before setting up his own teaching firm in Birmingham, where he was said to be living with a woman and her family in Winson Green.
The Department for Education has said he never held qualified teaching status and never taught in any state school in England.
At some point he was investigated by MI5 over links to violent extremism but was considered too minor to monitor, and did not feature on a 3,000-strong list of suspects feared to be capable of mounting an attack.
The suspected jihadi behind the attack at Westminster was radicalised in prison, it was claimed last night.
Neighbours said Khalid Masood returned from a spell behind bars obsessed with Islam.
He received his first conviction in November 1983 for criminal damage aged 18.
Then in July 2000, known by his birth-name of Adrian Elms, he slashed Piers Mott across the face after an argument at the Crown and Thistle pub in Northiam, near Rye, East Sussex, and spent two years in jail. One villager, who declined to be named, said: 'In prison he was radicalised by other inmates and converted to Islam. He became a real extremist.'
Mr Mott's widow, Heather Mott, said Masood had left her husband with a scar that stretched across his face from above his eye.
Speaking at her home, she said: 'It makes you feel sick. And it makes you feel even sicker when you think that was the guy who lived here. He was obviously prone to being radicalised. He has come out [of prison] even worse.'
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