The FBI has been involved in some wild cases in its history. Though evidence from more sensitive investigations may be classified, photos of many artifacts gathered by the bureau are in the public domain. From the polygraph machine used on an assassin's killer to a first-edition of Gone With the Wind with a hidden compartment, here are five of the most fascinating images you'll find in the FBI's photo archives.

1. First Edition Gone With the Wind

A first-edition copy of Margaret Mitchell’s Gone with the Wind is noteworthy in its own right, but this one contains a secret: a hidden compartment used to conceal a .32-caliber pistol. The FBI's Laboratory Division received this artifact in 1941, but they were unable to identify the weapon.

2. Forged Babe Ruth Baseballs

Federal Bureau of Investigations

These baseballs bearing forgeries of Babe Ruth's signature were recovered in Operation Bullpen. The mission was part of the FBI's crackdown on counterfeit sports memorabilia in the 1990s.

3. J. Edgar Hoover's Fedora

Federal Bureau of Investigations

J. Edgar Hoover served as the director of the FBI for nearly 48 years. This hat from the bureau's archives is emblematic of his signature G-Man style.

4. Pen Gun

Federal Bureau of Investigations

This artifact is exactly what it sounds like. Produced by an unknown maker in 1924, this small firearm is disguised to look like a normal ink pen.

5. Polygraph Machine Used on Jack Ruby

Federal Bureau of Investigations

This ordinary-looking Keeler model 6317 polygraph machine is a dark piece of American history. It was used on Jack Ruby, the man who shot Lee Harvey Oswald two days after Oswald killed President John F. Kennedy. Ruby asked for a polygraph test repeatedly to prove he was telling the truth about not being part of a larger conspiracy.