The driver then reportedly ran the few metres to the parliament complex and attacked a police officer with a knife before being shot by another officer.
Masood had rammed his auto into pedestrians on Westminster bridge on Wednesday injuring several people and later stabbed a police officer outside the British Parliament as he tried to enter the building. A total of nine persons remain in custody and one woman has been released on bail.
At Scotland Yard, headquarters of London’s Metropolitan Police, Acting Deputy Commissioner Mark Rowley, confirmed that the four dead were Constable Palmer, the terrorist, a woman in her mid-40s and a man in his mid-50s.
“The location of this attack was no accident”, May, dressed in black with a quavering voice, said outside her residence – a 10-minute walk from the scene.
Shortly before 15:00 UTC, multiple shots followed by screaming were reported outside London’s Houses of Parliaments.
The attack began early Wednesday afternoon as a driver in a gray SUV slammed into pedestrians on the bridge linking Parliament to the south bank of the River Thames.
Last July, another radicalised Tunisian, who like the London attacker was described by ISIS as one of its “soldiers”, ploughed a truck into crowds watching fireworks in the southern resort of Nice, killing 86.
The incident took place on the first anniversary of attacks by Islamist militants that killed 32 people in Brussels.
Authorities said Masood had prior convictions for violent offenses, including grievous bodily harm and assault, but was never convicted of terror crimes.
He said: ‘Muslim woman pays no mind to the terror attack, casually walks by a dying man while checking phone #PrayForLondon #Westminster #BanIslam’.
Police are still trying to pin down Massod’s preparation and movements before the attack.
The manager of the hotel said the terrorist had been “laughing and joking, telling us stories about where he lived”, hours before the atrocity.
Meanwhile, Prime Minister Malcolm Turnbull has assured the nation that the safety of its citizens is the utmost priority.
May told Parliament that the attacker “acted alone”, and there was no reason to believe there would be imminent further attacks.
Members of Parliament and Prime Minister Theresa May were spirited out of the building, and the Westminster Palace went on lockdown shortly after.
The BBC believes that Masood hired the vehicle used in the attack earlier this week from the Spring Hill branch of Enterprise in north Birmingham.
Among the injured are at least three French school teenage children.
Rowley said two police officers targeted in the attack have significant injuries.