Investigators now believe that the man responsible for the Westminster attack in March acted wholly alone in the planning and preparation for the first mass casualty terrorist atrocity to hit Britain in more than 10 years.
Initially investigators believed it was possible that the attacker, 52-year-old Khalid Masood, had encouragement, support or help in the planning, from someone else.
One source with knowledge of the investigation said: “The indications are he acted on his own, and that is rare.” The investigation of Masood is understood now not to be actively seeking anyone else.
Masood’s attack killed five people, injured more than 35 others, and ended with him being shot dead by a police officer before he could storm parliamentary buildings armed with two knives. Police made 12 arrests across Britain, including some at gunpoint. All those arrested were eliminated from inquiries, including his wife.
His preparations included driving to the area around the Palace of Westminster, central London, some days before the attack. He has now been identified as being behind the wheel of a vehicle moving around the parliamentary buildings about 96 hours before the atrocity, which he staged on 22 March this year. It is believed this action was reconnaissance.
Another source with knowledge of the inquiry added: “When it’s someone who is going to hire a car, they are not going to come across the radar as a concern to national security.”
Subsequent tracking via GPS has revealed the vehicle to have been in the Westminster area on Saturday 18 March, as first reported by the Wall Street Journal. The Guardian understands investigators have been using automatic number plate recognition technology and CCTV cameras to track the route that Masood took into the capital from a Brighton hotel he was believed to have stayed in.
Cameras are believed to have also shown Masood making the reconnaissance journey or test run. The visual match has led to the conclusion that it was probably Masood carrying out the scouting mission.
The investigation by Scotland Yard’s counter-terrorism command and MI5 has examined electronic items belonging to Masood. The inquiries are continuing.
The broader conclusion, that Masood acted without help to carry out an unsophisticated attack, has prompted fresh thinking by counter-terrorism officials about ways to improve the chances of stopping any similar atrocity.
Unsophisticated attacks like this can offer no clue that could lead to detection by police or MI5 beforehand – there are no communications to be intercepted.
Mystery still surrounds a WhatsApp message Masood sent minutes before starting the attack. The Guardian understands he sent a message, showing an interest in extremism, to a close acquaintance. That has been recovered by police.
Investigators said they had found no evidence of a direct link to Islamic State, which claimed the attack, nor that Masood had been directed to carry out the attack. It is believed he was inspired or encouraged by Islamist propaganda to attack the west, though.
The attack started when Masood drove into pedestrians on Westminster bridge before crashing the vehicle into railings. He then ran into the grounds of the Palace of Westminster, where he stabbed PC Keith Palmer to death. The rampage ended when he was shot dead by an officer.
Scores of armed officers were rushed to the area, with 50 present within 12 minutes. Police commanders feared the potential start of an assault on the heart of British democracy by armed terrorists.
Police chiefs said their armed response had improved since the 2013 terrorist attack in Woolwich, when it took 11 minutes to get the first firearms officers to the area. The first armed reinforcements at Westminster on 22 March arrived after one minute. In 12 minutes’ time more armed officers were present; these included counter-terrorist specialist firearms officers, bringing the total to 50. One senior source said: “Enough got there to engage a marauding, multi-pronged attack.”
In the immediate minutes after Masood struck, other important sites also had armed protection boosted. The second source said: “You don’t know what you are dealing with … there could be someone else in the car on the loose. Is this a lone actor? Are others about to attack? CCTV showed crowds of people running away from the vehicle.”
Several years ago Masood had featured on the periphery of a terrorism investigation, through an association with the suspect being investigated. But any risk Masood posed was thought to be too little to justify continued inquiries, compared with other people of interest to counter terrorism investigators.