Quote:Admit nothing
If you do a search on this quote, you'll get, "Shelly Laurenston, The Mane Event" as a citation from a book in 2007. Yeah, bullshit. That's a citation, but not the origin. I heard variations of this since the 1980's. Just because I can be quoted as saying, "The two most common elements are hydrogen and gullibility" doesn't mean I'm the origin. (OK. Techically, I replaced stupidity with gullibility, so I am an origin. But that's not the whole story).
The variation with "Admit nothing. Deny Everything. Make counter-accusations." (or the longer variant adds, "If calm is not to your benefit, chaos is your friend. And don’t trust anyone.") goes back to A New York Times article from 1987 quotes a person as saying he met someone in Nicaragua who bought a baseball cap with that slogan on it, at the CIA gift shop in Langley, Virginia. Which is quite likely, as the phrase seemed to be in common use. And there are dozen different variants of the ending. "Blame a Private" for military. "Find a scapegoat/patsy" in criminal and legal circles (same thing). And so on.