On that fateful night in 1865 at Ford's Theatre, Abraham Lincoln's sole bodyguard, Washington policeman John Frederick Parker, was supposed to be sitting outside the presidential box in a passageway behind the door. Trouble was, Parker couldn't see the stage from there, so he left his post to get a better view. This was after he was three hours late to relieve the previous bodyguard earlier in the afternoon.
Even worse, during the intermission Parker went out for drinks with the coachman and footman of Lincoln's carriage. He was not at his post when John Wilkes Booth entered the president's box.
Was Parker ever implicated in Lincoln's murder? Did he lose his job after this? What sort of employment record did he have before he received this prestigious assignment of guarding the president?
You can find the surprising answers in Paul Martin's article, "Lincoln's Missing Bodyguard," on the website for Smithsonian magazine.