It is well-known that Gates continued to associate with Epstein after the latter was convicted of procuring a child for prostitution. There doesn't really need to be anything else to the story in my opinion.
(Editing to be clearer: I don't think he is guilty of Epstein's crimes by association. I think he is guilty of associating with Epstein while being aware of some of his horrible crimes. I'm not saying he needs to be locked up over this, just that I don't trust him, and I question the judgment of people who do.)