At about 10pm,
Newbury started his conversation with Quentin, but was promptly knocked out.
A witness (apparently saw leaving the saloon shortly after Newbury; and then saw a scuffle between Stillwater and a few cloaked figures (who were carrying the unconscious Newbury). She screamed and ran for help.
Less than a minute later when the townsmen and sheriff arrive, Newbury and Stillwater are on the ground (Newbury unconscious and Stillwater dead), and their assailants (and Quentin) are nowhere to be found.
Stillwater appears to have been attacked by a something with claws (that may have carried some form of poison, perhaps a paralysis agent) that made a real mess of his torso. Additional, something seems to have held his head tightly whilst his brain was sucked out through his ear. His body also has traces of slime on it (presumably from his attacker), and his lucky tweed hat is gone.