The British man who killed four and injured 40 in Westminster yesterday was a middle-aged career criminal called Khalid Masood.
The 52-year-old "lone-wolf" attacker, who was living in the Birmingham area, has a series of convictions for assault and other crimes but police insist no intelligence suggested he was about to unleash a terror attack.
Kent-born Masood has never been convicted of terror offences, although Theresa May revealed this morning that he had been on MI5's radar a number of years ago.
Masood was a married father-of-three, an English teacher and a religious convert who was into bodybuilding, according to Sky News.
A Scotland Yard spokesman said this afternoon: "Masood was also known by a number of aliases. He was not the subject of any current investigations and there was no prior intelligence about his intent to mount a terrorist attack.
"However, he was known to police and has a range of previous convictions for assaults, including GBH, possession of offensive weapons and public order offences.
"His first conviction was in November 1983 for criminal damage and his last conviction was in December 2003 for possession of a knife. He has not been convicted for any terrorism offences."
Masood stabbed PC Keith Palmer to death with two knives outside parliament after killing mother-of-two Aysha Frade and US tourist Kurt Cochran as he ploughed along a crowded pavement on Westminster Bridge.
Giving details of the attacker's background in Parliament today, Prime Minister Theresa May said: "The man was British-born and, 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. Intensive investigations continue."
It is believed Masood had lived in the Winson Green area of Birmingham, where neighbours claimed he shared a flat with a woman and a young child.
Neighbour Iwona Romek, 45, said: "When I saw the pictures on TV and in the papers of the man who carried out the attack, I recognised him as the man who used to live next door.
"I would see him quite often, but it would just be a 'hello' and a 'how are you'. He had a young child, who I'd think was about 5 or 6 years old.
"There was a woman living there with him, an Asian woman. He seemed to be quite nice, he would be taking care of his garden and the weeds.
"He moved out in December. One day he was gone, there were delivery vans outside all of a sudden. Last night I just heard banging of the door and police shouting 'open the door, open the door'. They were saying 'it's on the second floor'.
"I heard the helicopters flying above too. Men were going in the forensics outfits, it was very strange. I just thought it was a normal family."
Earlier today, Middle East terror group Isis said: "The attacker yesterday in front of the British Parliament in London was a soldier of the Islamic State executing the operation in response to calls to target citizens of coalition nations."
Experts believe Masood did not receive direct orders from Isis but may have been inspired to carry out the attack by material online.
He was not on an MI5 list of 3000 people thought to be capable of mounting an attack, the Guardian reported.
The details of Masood's background will raise questions over what security officials knew about the assailant and what decisions were taken when he first appeared on the radar.
Armed police have arrested eight other people and raided six properties in London and Birmingham as they attempt to find any associates Masood may have had.
A neighbour of another property raided this morning says he believes Masood had been living there with another man.
Scotland Yard said that it was "not prepared to discuss" the operation coordinated with West Midlands Police, but a witness who works nearby said: "The man from London lived here."
The vehicle used in the attack was rented from a local Enterprise rent-a-car outlet.
A spokesman for the company said: "We can confirm that the car used in the tragic attack in London yesterday afternoon was one of ours.
"An employee identified the vehicle after seeing the licence plate in an image online. We ran another check to verify, and immediately contacted the authorities."
Speaking yesterday, Mark Rowley, the Met's senior anti-terror officer, said: "Hundreds of detectives have been working through the night and during that time I can confirm we have searched six addresses - and made seven arrests.
"The inquiries in Birmingham, London and other parts of the country continue. It is still our belief, which continues to be borne out by our investigation, that this attacker acted alone yesterday and was inspired by international terrorism.
"To be explicit - at this stage, we have no specific information about further threats to the public.
"Clearly our investigation is ongoing - developing all the time - and is focused on his motivation, his preparation and associates."