Earlier quoted context omitted.
If this were the case, they would provide him immunity in exchange for cooperation in prosecuting up the "food chain" like they do with mobsters.
I think this is just a thing that happens in the movies. Also, check out the source document and let me know if you think someone found guilty of the described acts deserves immunity.
Immunity can mean being convicted for lesser offenses, or negotiating a less than maximal punishment.