The fixing investigation appears to end 13 months after the fight, with a report of a conversation between an agent and a man who owned a card shop near Sonny Liston’s home in Denver. The shop owner claimed that “there was no doubt in his mind that Liston was at one time controlled by Philadelphia hoodlums,” though he seemingly had no evidence to back this up:

http://deadspin.com/the-fbi-spent-more-than-a-year-investigating-the-muhamm-1790931835