Roy R. Botello will never forget the crowd's enthusiasm the night he recorded a home movie of John F. Kennedy at a Houston hotel on the eve of the president's assassination in Dallas. The footage of a Nov. 21, 1963, gathering of the League of United Latin American Citizens shows Kennedy and his wife smiling as people jostle through the crowd to shake their hands or snap photos. A mariachi band can be seen behind the president and first lady. After keeping the silent, colour images he recorded stored away in a living room drawer in his San Antonio home...