Counter-terrorism investigators have been investigating Khalid Masood’s life and associations across Britain as they raced to discover what led him to kill four people and injure more than 50 in Wednesday’s murderous attack in Westminster.
A joint investigation by Scotland Yard’s counter-terrorism command and MI5 led to new arrests on Thursday in London, Birmingham and Manchester with two people still in custody, while properties were searched in Wales and southern England.
Police want to discover if Masood, who was shot dead by armed police, was encouraged, supported or directed in the atrocity. The 52-year-old mowed down people in the heart of London then stabbed a police officer to death as he tried to burst into the Palace of Westminster.
The Guardian understands detectives are scouring large amounts of CCTV camera footage to see if there is any recording of Masood scouting the Westminster area before the attack.
They are also using camera records and automatic number plate recognition technology to see if they show his car in the area, when Masood could have been working out where the best place to run people over might have been and what weak points there were in Palace of Westminster security in the run-up to the attack. They will also repeat the same time-consuming lines of inquiry to see if a possible accomplice may have done the same.
Two minutes before the attack started at about 2.40pm on Wednesday, Masood used the WhatsApp communications app on his mobile phone, although it is not known why.
On Friday police named Masood’s fourth victim as 75-year-old Leslie Rhodes. Two people remained in a critical condition in hospital.
MI5 is urgently trying to discover how someone could come to believe in Islamic State’s violent ideology and hatch a murderous plot against high-profile targets to gain worldwide attention, all without the domestic security service having any idea it was coming.
Fresh details about Masood’s life have emerged. He had a 20-year history of offending that saw him jailed at least twice. He had converted to Islam more than a decade ago, and used several names during his life, having been born as Adrian Elms and brought up as Adrian Ajao before adopting a Muslim name.
So far, police believe he acted alone when he drove a hired car into civilians on Westminster Bridge before running into the grounds of parliament and stabbing a police officer to death. It emerged that on the eve of the attack he had checked into a Brighton hotel under his own name. The hotel manager said that Masood had been “laughing and joking”.
Mark Rowley, Britain’s top counter-terrorism officer, said: “Whilst there is no evidence of further threats, you will understand our determination to find out if he either acted totally alone inspired by terrorist propaganda or if others have encouraged, supported or directed him.”
He described as “significant” two arrests made in Manchester and Birmingham.
Since the attack, police have arrested 11 people on suspicion of preparing terrorist acts. On Friday they released eight without charge, having eliminated them from their inquiries, and one woman was released on Thursday on bail. The two in custody are a 58-year-old man and a man aged 27, both arrested on Thursday in Birmingham.
An address searched by police in Carmarthenshire, Wales, is believed to be a farmhouse, belonging to his mother.
With key questions unanswered about the man who inflicted the worst mass casualty terrorist attack on Britain in more than a decade, Rowley said investigators needed help from the public.
“We remain keen to hear from anyone who knew Khalid Masood well; understands who his associates were; and can provide information about places he has recently visited,” he said.
“There might well be people out there who did have concerns about Masood but weren’t sure or didn’t feel comfortable for whatever reason in passing information to us.”
The man described Isis propagandists as a “soldier” in their campaign of violence was born Adrian Elms, and the Guardian has established he grew up in Tunbridge Wells, Kent, with two half-brothers.
But in 2000 he was jailed for grievous bodily harm after stabbing a man in the face following a row that was reported at the time to have had racial overtones. After being released from jail he attacked someone else and was imprisoned again.
Seventeen people are still being treated for their injuries in five London hospitals. Two of those are in critical condition, according to the Metropolitan police, with one person’s injuries considered life-threatening. One police officer struck on the bridge, PC Kris Aves, 35, is feared to have suffered severe injuries.
More than 50 people, of at least 12 nationalities, were injured in Masood’s attack on Westminster Bridge. Of these, 31 initially required hospital treatment.
One woman rescued from the Thames, Andreea Cristea, 29, from Romania, was in London with her fiance, who had been planning to propose to her. Masood’s car struck her, throwing her into the river. She underwent an emergency operation for a blood clot on the brain.
Prince Charles visited some of the injured in hospital as police named the fourth dead victim of Masood’s attack. Rhodes, of south London, died in hospital overnight from his injuries sustained on Westminster Bridge. The others killed in the attack were PC Keith Palmer, 48, who was fatally stabbed by Masood inside the parliamentary gates; Kurt Cochran, 54, an American tourist, and Aysha Frade, 43, a London teacher. An internet fundraising appeal for Palmer’s family has raised more than £600,000.
Past terrorist attacks in Britain have led to debates about new laws or initiatives to counter the lure that violent jihad has for a small number of British based people.
Pent-up anger among law enforcement and government has spilled over, with Downing Street demanding social media companies do more to expunge extremist material from the internet. The prime minister’s spokesman said firms such as Facebook and Google “can and must do more” to remove inflammatory material from the web and that it was up to them to respond to public concern.
“Social media companies have a responsibility when it comes to making sure this material is not disseminated and we have been clear repeatedly that we think that they can and must do more,” the spokesman told journalists.
“We are always talking with them on how to achieve that. The ball is now in their court. We will see how they respond.”
In the aftermath of the attack, hundreds of people were rushed into Westminster Abbey, which was used as a sanctuary in case of further attacks. On Friday the Archbishop of Canterbury and Muslim leaders were among those who joined an interfaith service to remember the victims of Masood.