Bobby Dunbar (Louisiana, 1912)

Fans of This American Life will recognize this story, as it was the center of one of the show's best episodes. When young Bobby Dunbar, just 4 years old, wandered off from his family on a group outing, he was never seen again. It's possible he fell from a railroad trestle and drowned. It's also possible he was abducted by a "strange man" who was seen lurking in the area. But we'll likely never know, because authorities thought they found Bobby Dunbar — and didn't realize it was another child entirely (who simply stepped into Bobby's life) until 2004, long after it would have been possible to solve the case.