Khalid Masood, 52, the man behind the terror attack on Westminster in central London, is the subject on an intense police investigation which has seen nine people arrested throughout the UK since Wednesday.
Originally named Adrian Russell Ajao from Kent, Masood is believed to have mostly lived in the West Midlands and the city of Birmingham in central England.
Although he was known to police in the UK, intelligence officers did not consider him to be a criminal posing any immediate threat.
Scotland Yard on Friday urged members of the public who knew Masood to step forward with any information which could help in their investigation, which is focused on understanding his inner circle and possible network.
“Our investigation focuses on understanding his motivation, his operation and his associates,” said Mark Rowley, Britain’s senior counterterrorism police officer.
Police are actively attempting to piece together whether Masood, a Briton-born Muslim convert, acted alone in carrying out his attack and whether he was radicalised by Islamist terror propaganda.
“Whilst there is still no evidence of further threats, you’ll understand our determination is to find out if either he acted totally alone, was inspired perhaps by terrorist propaganda or if others encouraged, supported or directed him,” Rowley said.
Masood killed four people including a police officer guarding the UK parliament on Wednesday in what has been the UK’s worst terror attack since 2005.
Scotland Yard has said it suspects Masood was inspired by international terrorism.
ISIL on Thursday claimed responsibility for the attack.
A US government source, speaking to Reuters on condition of anonymity, said some people Masood was involved with are suspected of having wanted to join jihadi groups abroad, but that Masood himself “never did so”.
Since his identity was revealed, Masood’s background has been highly scrutinised.
According to the Huffington Post, Masood had several aliases and was also known as Adrian Elms.
The Post reports Masood lived in Saudi Arabia in 2005 where it is believed he became a self-styled English tutor.
He is thought to have returned to the UK the following year, but had returned to Saudi Arabia between 2008 and 2009, the Post reported.
By 2012 Masood was back again in the UK and had set up a tutoring business in Birmingham.
Born on Christmas Day in 1964, he is thought to have been mostly raised by his single mother.
His first criminal conviction came in 1983 when he was found guilty of causing criminal damage. His last conviction came 14 years ago in December 2003 for being in possession of a knife, according to Reuters.
The BBC reports Masood also spent two years in jail after he admitted to attacking a man with a knife in a pub.
He had never been convicted of a terrorism-related offence.
Little is also known of Masood’s private life.
Media reports say he described himself as a former teacher who was into bodybuilding, said Reuters.
According to a former neighbour, Masood may have been a father.
“He has a young child, who I’d think was about five or six years old. There was a woman living there with him, an Asian woman,” said neighbour Iwona Romek, 45, to Reuters. “He seemed quite nice.”
Others, however, called Masood “the vampire” because he would go out at night dressed in black, reported the BBC’s security correspondent Frank Gardner on Thursday evening.
UK Prime Minister Theresa May on Wednesday told MPs in Parliament Masood had been previously investigated by MI5 for “concerns about violent extremism”. She described him as a “peripheral figure” in a historic case and that there was “no prior intelligence of his intent” of carrying out an attack in the UK.
Masood’s actions on the day of his attack remain partially obscured.
What is known is that in Birmingham he hired the Hyundai he would eventually use to carry out his attack.
Investigators have not yet pieced together where Masood went, who he talked to or what might have happened between Birmingham and London leading up to his attack.