Key Witness (1947)

Milton Higby, an inventor of gadgets that don't sell finds himself accused of a crime he didn't commit---the killing of a girl he had just met---, and takes to the open road with the police in close pursuit. In his travels, he stumbles across the body of another murder victim and switches identities with the corpse. With his new name he poses as the long-lost son of a wealthy industrialist until he is exposed and charged also with the second murder.