1927: On 27 September, Police Constable George Gutteridge was murdered on a country road in Essex. In the small hours, Gutteridge flagged down a Morris Cowley, unaware that it had been stolen earlier that night. While he questioned the two men in the car, Frederick Browne and William Kennedy, one of them pulled a revolver and shot him in the side of the face. (Kennedy subsequently blamed Browne; Browne denied he was even there.) As the policeman lay badly injured in the road, the gunman approached and finished him off with two shots at close range – one in either eye.
Source: Christopher Berry-Dee and Robin Odell, The Long Drop: Two Were Hanged – One Was Innocent (1993)