LONDON, ENGLAND - MARCH 23: A police officer lays a floral tribute given by a member of the public beside a photo of PC Keith Palmer, the policeman who was stabbed to death as he guarded the Palace of Westminster from a terrorist in yesterday's attack on March 23, 2017 in London, England. Four people have been killed and around 40 people injured following yesterday's attack by the Houses of Parliament in Westminster. (Photo by Jack Taylor/Getty Images)
