One thing about Fosco's current contentions: No matter who potentially flips, it's extremely difficult to get a murder conviction without a body, weapon or other corroborating evidence. One guy's testimony is generally never enough, and was (at least the rumored) reason they didn't indict DiFronzo for the Spilotro murders based on Calabrese's testimony alone back during Family Secrets.

I don't know anything about the case they're talking about but I'm assuming it's decades old and nothing like that is going to be around.

Cops often "know" exactly who did what, they just can't prove it.

Fosco knows that, of course.