Assassination Trivia

[RJNorton]

People who believe it was not John Wilkes Booth at Garrett's can point to a statement made by a person who said the man accompanying David Herold wore a slipper on his right foot. The implication is that the injured leg was the right one, not the left. This does not match Booth's injury, and therefore could not be Booth who was riding with Herold.

What is the name of the man who said the man with Herold was wearing a slipper on his right foot?