British authorities on Monday identified two men who were shot dead by police in the minutes following a terrorist assault on London Bridge over the weekend.
Butt was 27 and a British citizen born in Pakistan. Rachid Redouane - who had claimed to be Moroccan and Libyan, variously gave his age as 30 or 25 and also used Elkhdar as a surname - was not on the radar of police or intelligence agencies until the attack.
Butt, who is thought to have also gone by the name Abu Zaitun, was known to neighbours by the nickname "Abs/z" and was allegedly an associate of radical hate preacher Anjem Choudary.
Police said they were still working to establish the identity of the third attacker.
The Commissioner said it was a "high priority" for officers to understand whether they had help from anyone else in the planning of the attack.
Eighteen are still in hospital in critical condition, according to an update by Britain's National Health Service. Trump has used the policy, stalled now in U.S. courts, as an example of the sort of toughness that he says Khan refuses to show amid terrorism attacks that are riling the United Kingdom.
"Our city has suffered two very bad terrorist attacks since I was elected as mayor - and we must do everything possible to stop there being any more", he said.
An Irish security source described the murderer as having "extensive immigration history related to the UK".
NBC News reported Monday that an American bystander was shot in the head by a stray bullet fired by police toward the attackers during the incident on London Bridge and in nearby Borough Market on Saturday night.
ISIS said its "soldiers" carried out the attack.
Jeremy Corbyn, leader of the main opposition party, called on May to resign over the issue, saying earlier that "you can not protect the public on the cheap", and promising to recruit another 10,000 police officers if he is elected into power.
The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group claimed responsibility for the attack. "We said we had just been standing there", said Berry.
In a brief speech at the vigil, London Mayor Sadiq Khan seemed to speak for many as he voiced his sorrow and anger.
Before the origins of the London Bridge attack were even clear, Trump seized on it to promote his order restricting travel from Muslim-majority nations and lament that the Supreme Court is reviewing a "politically correct version".
Khan, the first Muslim mayor of a major western capital, said the Islamist extremists who targeted civilians in bars and restaurants were despicable and the city would be resilient in the face of the attack.