Definitely the Lindbergh kidnapping and murder. I think the extortion was separate from the kidnapping, and Fisch and possibly Hauptmann took part in that. Thanks to Lindbergh, the symbol on the ransom note found in the nursery was circulating in the underworld very quickly, so it was very easy for someone to fake letters. IMO much of the evidence against Hauptmann was faked by the police, i.e. the attic board, Condon's phone # in a closet. (Someone on this thread mentioned that Hauptmann had held up a woman and a baby in Germany--I think it was actually a woman pushing a baby carriage in the days when inflation required Germans to pay for groceries with enormous amounts of cash.) Lindbergh's behaviour throughout was suspicious, and the revelation of his post-war secret families indicates the big divide between his public persona/real self. He was notorious for cruel and life-threatening "jokes": one of Betty Gow's first actions was to ask him if he had the baby and there is a claim that he had hidden the baby in a closet previously and put the household in an uproar. He claimed to have heard a noise like an orange crate breaking (which he didn't investigate) and testified that Hauptmann's voice was the same as Cemetery John's (having heard him say 3 words several years before)--odds are that his hearing had been badly damaged through years of unprotected open-cockpit flying. Many are of the opinion that Lindbergh's testimony put the final nail in Hauptmann's coffin. IMO Lindbergh is an excellent suspect.