Police released his name as Khalid Masood but the terrorist who slaughtered innocent victims was born Adrian Elms, a career criminal with a history of violent knife crime.
He went off the rails in July 2000, slashing a man across the face after an argument that had "racial overtones". The attack would land him in jail and his life, already in a fragmented state, would fall apart. In another attack three years later, he stabbed a man in the nose.
The extraordinary revelations will cause deep unease. Elms – or Masood, the Islamic name he adopted – was known to the authorities as a vicious thug whose ‘violent extremism’ had brought him to the attention of MI5. Yet at some point a decision was taken that he was no longer considered a threat.
On Wednesday, having stayed the night before the attack in a cheap hotel in Brighton, he got into a hired car, drove to London and then used it as a weapon to kill pedestrians on Westminster bridge.
Then brandishing a knife, he slaughtered a police officer, trying to protect the palace of Westminster, in cold blood.
Masood told staff at the Preston Park Hotel: “I’m off to London today” as if he was a tourist. The capital, he declared, “isn’t like it used to be.”
Masood was 35 and living in the quiet Sussex village of Northiam when in 2000 he slashed a cafe owner in the face with a knife after a row that had ‘racial overtones’. Masood, whose mother was white and father black, was born in Dartford in Kent.
Masood, one of only two black men Northiam - according to a court report at the time - was ostracised from the community. He was jailed for two years for the attack.
Three years later and now out of jail, Masood was accused of stabbing a man in the nose, leaving him needing cosmetic surgery. He was sent back to jail for another six months for possession of offensive weapon. He served time in Lewes jail, East Sussex, Wayland prison in Norfolk, and Ford open prison, West Sussex.
It is quite likely he was radicalised during a spell in jail.
By 2005 he was working in Yanbu, Saudi Arabia, then teaching workers at the General Authority of Civil Aviation (GACA) in Jeddah, according to The Sun, which says it obtained a copy of Masood's CV.
Theresa May, in a statement to MPs at 10.30am on Thursday, was quick to absolve her security services of blame.
“His identity is known to the police and MI5 and, when operational considerations allow, he will be publicly identified,” she said.
“What I can confirm is that the man was British-born and that – some years ago – he was once investigated in relation to concerns about violent extremism. He was a peripheral figure. The case is historic – he was not part of the current intelligence picture.
“There was no prior intelligence of his intent or of the plot.”
Five hours later, the Metropolitan Police made public one of his adopted names – Khalid Masood- in a short statement that gave scant details of his long history of violent crime. None, they stressed, were for terrorism offences.
Masood, a burly bodybuilding enthusiast, received his first conviction in November 1983 for criminal damage when he was 18 and his last one in 2003 for possession of a knife.
In a 20-year criminal career he also received convictions for causing grievous bodily harm.
He has lived a nomadic existence including stints on the south coast as well as in Kent.
It is thought that after his time in prison, he came onto MI5’s radar. A Whitehall source said he had been a person of interest but “peripheral” to a terror investigation. The source declined to identify the terror cell.
Over the past five or six years, Masood, his wife, aged 39, and their young children, have been on the move. Electoral roll records show him living in areas notorious for pockets of Islamist extremism.
He lived for more than two years until 2013 in Luton, where Anjem Choudary, an influential preacher now in jail for terror offences, had been a regular and often mob-handed visitor.
A former neighbour in Luton, Katie Garriques, 48, a former headteacher, remembered a “polite, shy” and “quite portly man” whom she often saw gardening at the front of the property and playing with his children.
When she saw the photograph of Masood having been shot in Westminster, she recognised him instantly. “I’m just saddened. I feel sick to be honest,” she said.
Monica, another neighbour in Luton, said she only ever saw him at night. “He was like a shadow, you wouldn’t often see him. He was often in Islamic dress,” she said.
From Luton, Masood and his family moved to Forest Gate in east London. A neighbour, who asked not to be named, said Masood frequented a mosque in nearby Leyton. Another neighbour, Ibrahima Kone, 57, a cab driver, said the family lived there for three years. At some stage Masood’s wife had moved to a new property on the site of the Olympic Village. A property there was raided by police on Wednesday night.
In the past year, Masood and his family moved to Birmingham to a block of flats at Quayside in Winson Green. It is not clear why they moved there, but that property was also raided by anti-terror police following the attack.
Student Kaodi Campbell, 25, confirmed the man in the picture was her neighbour. “He was always polite and would say ‘hello, hello’ to me,” she said.
“You could tell they were religious, his wife always wore traditional dress. I last saw them just over a month ago. They had three children. He had a job and you would see him leaving for work or taking his children to school.”
Local children remember him joining in games of football. One boy said: “Sometimes he’d play as well, though he wasn’t very good. He wore a skull cap and had a long bushy beard.”
On Monday or Tuesday, Masood turned up at the car hire company Enterprise at its Spring Hill depot in Birmingham and rented the Hyundai SUV used in Wednesday’s attack.
He gave his profession as a teacher and, it is understood, his address as a rented flat close to Edgbaston and not far from the Enterprise offices. On Wednesday at 11pm, armed police stormed the upstairs flat at Hagley Road. More than a dozen officers armed with machine guns stormed the premises, making three arrests. One witness, who works in a shop near the second-floor flat, said: “The man from London lived here. They came and arrested three men.”
Scotland Yard said on Thursday it had made eight arrests, seven in Birmingham and one in east London of a 39-year-old woman. A property in Brighton, where The Sun reported Masood spent his last night, and another in south-east London were also searched.
David Videcette, a former Scotland Yard counter-terrorism officer and security expert, said it was odd that Masood had committed the atrocity at the age of 52.
“His age is surprising as most terrorists are radicalised at a much younger age,” said Mr Videcette. “It would be my assessment that he has probably had quite a troubled past, with involvement in drink or drugs leading him into criminality.
“Then at some point, possibly in the last decade, he has converted to Islam and changed his name. Then it appears that he has fallen under the malign influence of others who have encouraged or persuaded him to carry out this attack, possibly for money for his family.”
Mr Videcette added: “What will be key is establishing why he has suddenly and quite recently moved to Birmingham, having spent most of his life in the South East.
“Pretty much every terror case I worked on had some Birmingham connection somewhere along the line. It is likely there were people there who were part of his close circle and the police will want to look at that aspect very closely indeed.”