Karpis wasn’t actually one of Ma Barker’s four sons but it was after he met her youngest, Fred, that the family gang became a federal concern. Karpis suggested the kidnap of a banker but he was the son of a friend of President Roosevelt.
This made them Public Enemy No1 to director and founder of the FBI, J Edgar Hoover. Karpis wrote to Hoover promising to kill him.
Instead, months later, he was stopped and surrounded by a dozen agents so that Hoover himself could walk up and make the arrest...