Why did the FBI investigate John Wilkes Booth more than 75 years after his death?

Admit it — if you’re a lover of history, you probably believe that reading something especially intriguing can transport you through time. I have that experience almost every time I browse FBI files on notable people and events.

Over the years, in response to Freedom of Information Act requests, the FBI has publicly released its files on a marvelous assortment of deceased people of celebrity, infamy, and importance. On my personal blog, I’ve written about the FBI file on the actress Carole Lombard and the agency’s investigation of the World War II air crash that killed her, as well as the file on architect Frank Lloyd Wright and his tangles with the government.

These files reveal as much about the worldview and techniques of the FBI as they do of the lives of their subjects.

A few years ago I learned that John Wilkes Booth, who assassinated Abraham Lincoln in 1865, is the subject of another bulky FBI file, which is surprising because the FBI did not come into existence until six decades after Booth’s crime and death. What could possibly be in a file compiled so long after Lincoln’s assassination?

Did Booth elude capture?

The oldest pages of the file discuss the possibility that Booth escaped capture after…