The moment 29-year-old British citizen Salih Khater drove his silver Ford Fiesta into the car-proof security barrier guarding Westminster's Houses of Parliament was captured on a rooftop camera.
Footage obtained exclusively by the BBC and shared on social media shows a van driving down the same road as Khater, pulling into the same lane moments before he rams the car into barriers, injuring three cyclists.
The van then drives in the direction of Khater's car, but gets stuck in traffic while the Ford Fiesta crashes into the barrier.
A spokesperson for London's Metropolitan Police told journalists the mysterious van "was not of interest" but speculation over why it was there behind the suspect's car had already started brewing on Twitter.
One theory, however, is that the van was being driven by police officers, meanwhile, Scotland Yard's Assistant Commissioner Neil Basu has said "There wasn't a police car in pursuit of the vehicle."
Former counterterrorism officer and detective David Videcette thinks otherwise and tweeted: "The consensus between those of us who are ex-Police, is that this is likely an unmarked police vehicle, who spotted the Fiesta acting strangely before it rammed the barrier."
The silver van carries out on following the fiesta where ever it goes. Then at 1.28 on the video it overtakes the other vehicle it’s caught behind. pic.twitter.com/VvuCfk6GHl— David Videcette (@DavidVidecette) August 14, 2018
It’s seen here at the front of the queue after the accident.— David Videcette (@DavidVidecette) August 14, 2018
The consensus between those of us who are ex-Police, is that this is likely an unmarked police vehicle, who spotted the Fiesta acting strangely before it rammed the barrier. pic.twitter.com/QLFh6yAV5J
Former head of counter-terror at MoD tells @skysarahjane that police have “over and covert” teams in place but can’t comment specifically on the ‘mystery van’ identified trailing behind #Westminster crash vehicle.https://t.co/2SGCf7VlZS— Tom Macleod (@SkyNewsTom) August 15, 2018
In today’s #Westminster incident the attacker car is seemingly being followed by a van. Many possible explanations, but note police say not of interest but don’t say why, and while denying it’s police don’t confirm not others eg mi5pic.twitter.com/2tK8oKma33https://t.co/OuPmDQ9Xgi— Charles Shoebridge (@ShoebridgeC) August 14, 2018