FBI Agent Bill Roemer chased The Outfit for 22 of his 30 years in the bureau. He wrote a detailed book about the Outfit and Tony Accardo shortly before he died.
https://www.amazon.com/Accardo-Godfather-William-Roemer-Jr/dp/0804114641/ref=sr\_1\_1?qid=1645591157&refinements=p\_27%3AWilliam+F.+Roemer+Jr.&s=books&sr=1-1&text=William+F.+Roemer+Jr.
Accardo: The Genuine Godfather