Analysis | How one man brought terror to heart of London with a car and knives

Prime Minister Theresa May had just cast her vote for a pensions bill when she was told the UK Parliament was under attack.

Minutes earlier, the tourists that throng Westminster Bridge, taking selfies in front of Big Ben, had scattered as a car careened down the sidewalk toward them, before crashing into the railings next to the famous clock tower.

There were shouts as the driver jumped from the wreckage and ran through the crowds around the corner toward the huge iron gates of Parliament that are supposed to keep intruders out.

Those gates have to be kept at least partially open when lawmakers are voting, to allow them to get into the building before the vote is over. They’re guarded by police whose days are generally spent giving directions and posing for photos with tourists.

Police officer Keith Palmer - who was unarmed - tried to stop the intruder. He was stabbed. A plain-clothes colleague shouted a warning to the attacker, and then opened fire with a gun. He fired several times. Journalists with offices in Westminster, could see the events unfolding outside their window.

Moments later, the wounded policeman and the assailant were both lying on the cobbles outside Parliament. One officer with a sub-machine gun kept it aimed at the downed attacker, while his colleagues tried to keep him alive.