The Islamic State group has claimed responsibility for an attack by a man who plowed an SUV into pedestrians and then stabbed a police officer to death on the grounds of Britain's Parliament.
More than 50 people of a dozen nationalities were injured, 31 of whom required hospital treatment.
A British-born former teacher and Muslim convert, Masood had shown up on the periphery of previous terrorism investigations that brought him to the attention of Britain's MI5 spy agency.
People lay flowers as a tribute to the victims of Wednesday's attack outside the Houses of Parliament, after police cordon was removed in central London, Thursday March 23, 2017. "That understanding may have died with him", he added.
Known by a number of other aliases, he racked up a string of convictions, but none for terrorism-related offences.
Masood was staying at a hotel in Brighton since Tuesday and, according to the hotel's manager, he was "laughing and joking" in Brighton the night before making his fatal journey to London. Two people are still in critical condition and one has life threatening injuries, Rowley said.
Pc Kristofer Aves was returning from a ceremony where he collected a commendation for his work as a family liaison officer when he was seriously injured as Khalid Masood drove his hire vehicle into pedestrians on the bridge on Wednesday.
In a statement late Saturday, the Metropolitan Police's Counter Terrorism Command revealed that 82 seconds passed from the moment on March 22 when Khalid Masood rammed his auto into pedestrians and then exited the vehicle to attack police with a knife, until the moment he was shot dead by officers.
A 35-year-old man and a 32-year-old woman were arrested at separate locations in Manchester on Friday.
Mark Rowley revealed the name in a briefing outside Scotland Yard in which he also announced two more "significant" arrests had been made.
The attacker was born in Kent and lived in West Midlands, according to Metropolitan Police.
The police also named the 75-year-old victim killed in the deadly attack as Leslie Rhodes from south London.
Although 11 people were arrested in the aftermath of the attack, nine have since been released, with no further action to be taken. His last came 14 years ago in December 2013 for possession of a knife.
Police are investigating media reports that Masood checked his encrypted messaging service WhatsApp - or even sent a message - just before the attack, which hinted at others being involved.
"An act of terrorism tried to silence our democracy", May told parliament.