LONDON, ENGLAND - MARCH 22: Police investigators seen on Westminster Bridge on March 22, 2017 in London, England. A police officer was stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard also reported an incident on Westminster Bridge where one woman has been killed and several people seriously injured by a car. (Photo by Carl Court/Getty Images)
LONDON, ENGLAND - MARCH 22: Ambulances, police vehicles and emergency services seen on Westminster Bridge on March 22, 2017 in London, England. A police officer was stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard also reported an incident on Westminster Bridge where one woman has been killed and several people seriously injured by a car. (Photo by Carl Court/Getty Images)
LONDON, ENGLAND - MARCH 22: An armed police officer stands guard near Westminster Bridge and the Houses of Parliament on March 22, 2017 in London, England. A police officer has been stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard report they have been called to an incident on Westminster Bridge where several people have been injured by a car. (Photo by Jack Taylor/Getty Images)
LONDON, ENGLAND - MARCH 22: A member of the public is treated by emergency services near Westminster Bridge and the Houses of Parliament on March 22, 2017 in London, England. A police officer has been stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard report they have been called to an incident on Westminster Bridge where several people have been injured by a car. (Photo by Carl Court/Getty Images)
LONDON, ENGLAND - MARCH 22: Commander BJ Harrington of the Metropolitan Police makes a statement outside of New Scotland Yard on March 22, 2017 in London, England. A police officer has been stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard report they have been called to an incident on Westminster Bridge where several people have been injured by a car. (Photo by Jack Taylor/Getty Images)
