British police confirmed that the responsible for Wednesday terrorist attack on Westminster as Khalid Masood, a 52-year-old ex-convict born in Kent who used a string of aliases and reportedly converted to Islam only in later life.

Masood was described by police as a criminal with a 20-year record of offending, who had once been investigated for extremism but was assessed as low risk. Reports have emerged that his birthname was Adrian Elms.

While police investigate terrorist Khalid Masood, death toll in the attack rises. The death toll from his assault on the capital rose to four on Thursday night when a 75-year-old man, who has not been named, died at King’s College Hospital.

Five others remain in a critical condition after Masood drove his car into pedestrians on Westminster Bridge before running into the parliamentary estate armed with two knives and fatally stabbing a police officer before himself being shot dead.

On Thursday night, thousands of people gathered to commemorate the victims of the attack in Westminster, and to hear speeches by the capital’s mayor and other leaders aimed at preventing terrorism from spreading division and hatred, as reported in The Guardian.

Earlier in the day, prime minister Theresa May told MPs Masood had been previously known to MI5: “Some years ago, he was once investigated in relation to concerns about violent extremism. He was a peripheral figure. The case is historic – he was not part of the current intelligence picture.”

 Prime Minister Theresa May urged citizens to go about their lives as usual—a philosophy of resilience that’s carried the U.K. through war and terror in the past, as reported in The Atlantic. In the aftermath of the 2005 London bombings, which killed 52 commuters and injured hundreds of others, British Prime Minister Tony Blair delivered a statement from his office at 10 Downing Street in which he paid tribute to two very specific qualities of Londoners—their “stoicism and resilience,” vowing that citizens would “hold true to the British way of life.”

 Those past attacks also shaped London’s emergency response system, which showed on Wednesday it was well prepared for the attack. 

The Muslim Council of Britain and other UK Muslim leaders, which condemned the attack and offered prayers for the victims on Wednesday, issued a further statement on Thursday praising the Met police, the prime minister and the mayor of London.

The group’s general secretary, Harun Khan, said: “This attack was cowardly and depraved. There is no justification for this act whatsoever. The best response to this outrage is to make sure we come together in solidarity and not allow the terrorists to divide us.