My guess is that all of the clubs were heavily infiltrated.
The whole thing was likely started by an agent/provocateur un-holstering his piece as a psychological signal that it was time to rock and roll, but possibly not actually firing a shot.
Probably not all of them, but the Cossacks for sure, and probably the Bandidos. Some of the "criminal gang" clubs represented with members at Twin Peaks that Sunday have very few members, and didn't even register on LEO radar.
-- The whole thing was likely started by an agent/provocateur un-holstering his piece as a psychological signal that it was time to rock and roll, but possibly not actually firing a shot. --
That's possible, and so is even less direct provocation. Manson didn't kill anybody, he manipulated followers to perpetrate murder.