The FBI was born out of a trumped and trumpeted BS case. The "Kansas City Massacre" was the impetus to expand a small, unarmed, group of 14 federal agents into the FBI. The massacre occured when 3 Thompson equipped men, one of whom was reportedly Maching Gun Kelly, attempted to break a prisoner out of the custody of 7 state and federal officers. Apparently, one of the feds paniced and negligently discharged his shotgun into the back of the prisoner's head and them proceeded to blast wildly, killing another 2 agents. All 5 killings were blamed on the 3 "liberators," ignoring the fact that all but 1 death resulted from shotgun wounds.
Kelly denied (his only written denial of a killing) involvement up to the moment he was killed (some say executed) in a field by Melvin Purvis. One of the other two men was found, beaten to death, in a roadside ditch. The final "liberator" was caught, convicted, and executed, much to the delight and credit to the new FBI.
If I remember correctly, it was 3 or so years between the FBI charter and the apprehension/deaths of the 3 "liberators."