On Thursday, London's Metropolitan Police identified 52-year-old Khalid Masood as the Muslim man behind Wednesday’s deadly terror attack in Westminster.

According to British authorities, Masood rammed his SUV into dozens of pedestrians on Westminster Bridge before exiting his vehicle and stabbing a police officer outside of the gates of Parliament. Four people were killed during the rampage; at least 40 others were injured. Seven of the victims remain in critical condition. The attacker was shot three times by plainclothes officers after he refused to put down his knife. He later died of his injuries.

Details are only now emerging about the attacker’s identity. Here’s what you need to know about Khalid Masood:

1. Masood was a native of England. He was born in Kent, in southeast England. He moved to Birmingham in December and lived in a new-build house. Birmingham is home to a large Muslim immigrant population.

As the father of three young children, he reportedly put on the “façade of respectable suburbanite,” according to The Independent.

“He washed his car, mowed his lawn,” neighbor Ciaran Molloy told The Independent. “He was quite friendly, polite in every interaction.”

2. Masood had a long criminal record. “He had a record of convictions, stretching from 1983 to 2003, for assault, weapons possession and violations of public order,” reports The New York Times, adding, "But he was not the subject of any current investigation, and 'there was no prior intelligence about his intent to mount a terrorist attack,’ the London police said." Masood was convicted most recently in 2003 for possession of a knife. During his stint in prison, he reportedly stabbed a 22-year-old in the face.

3. Masood claimed that he was an English teacher in order to rent the vehicle that would ultimately be used in the fatal attack on Westminster. “Hiring the 4x4 Hyundai from the rental firm Enterprise in Spring Hill, Birmingham, he told them he was an English teacher – a claim that has yet to be verified, but may be unlikely given his criminal convictions,” reports The Independent. “Masood also told the car hire firm something else – he called the company to say he was likely to cancel the hire.”

4. Police believe that Masood “acted alone,” however, he “was inspired by international terrorism.” It’s unclear what the Metropolitan Police mean when they say that he was “inspired by international terrorism.” Yet, both Prime Minister Theresa May and defense minister Michael Fallon have confirmed that the attack on Westminster was indeed a terrorist incident. Authorities are investigating accordingly, looking at possible links to local and global terrorist networks. Masood was known for using a number of aliases during his flirtations with radical Islam. He may have been radicalized behind bars.

5. Masood was known to British intelligence as a “peripheral figure” when it came to “violent extremism.” In a speech to the House of Commons, Prime Minister May divulged only surface-level information about Masood’s possible links to Islamic jihadism.

“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,” she stated. “He was a peripheral figure.”

May stressed, “There was no prior intelligence of his intent – or of the plot.”

6. Seven people have been arrested in relation to Wednesday’s attack. Hundreds of detectives swarmed six addresses in a massive pre-dawn raid in Birmingham early Thursday. Police knocked down several doors and closed down streets in a formidable show of force. Here’s a list of the individuals detained under the Terrorism Act, according to the BBC:

  • A 21-year-old woman and a man, aged 23, were arrested at an address in Birmingham
  • A 26-year-old woman and three men aged 28, 27 and 26 were arrested at a separate address in Birmingham
  • A 58-year-old man was also arrested on Thursday at a separate address in Birmingham on suspicion of preparation of terrorist acts
  • A woman, aged 39, was arrested in east London

7. ISIS has claimed responsibility for the attack, calling Masood “an Islamic State soldier."

"The perpetrator of the attacks yesterday in front of the British Parliament in London is an Islamic State soldier and he carried out the operation in response to calls to target citizens of the coalition," a statement issued by ISIS' propaganda channel, Amaq read. Other unofficial pro-ISIS telegrams and posts have praised the attack in London as a victory for Islam.

ISIS has all but standardized its largely recycled statements claiming responsibility for large-scale, high-profile attacks on the West. The phrase “soldier” of the Islamic State is commonly used by Amaq news for jihadists who have been influenced by ISIS propaganda. The term doesn’t necessarily mean that the martyred jihadist was in direct contact with the terror group.

It’s important to note, however, that there’s ongoing investigation into Masood’s potential terrorist affiliations. British intelligence services are scouring recent contacts in Birmingham and elsewhere to determine how much contact (if any) Masood may have had with sleeper cells embedded in the U.K. and Europe.