J. Edgar Hoover didn't pursue them and allowed them free rein.
The mob had evidence that Hoover liked to wear the old panties from time to time. Literally.
Bobby Kennedy was the first high ranking cop at the federal level to go after the mob.
I don't know for sure about the panties, but I know that there was a conversation recorded (Angelo Bruno, IIRC) where some mob guys said Hoover was a so called "fairy". Their word, not mine. So the rumors about him and Clyde spread far outside of Washington, D.C. In any case, Hoover was too busy chasing (mostly imaginary) Communists to give a shit about organized crime.
