Bill Cosby Juror Harrison Snyder says Comedian's Words Sunk Him

Bill Cosby fell on his sword the moment he opened his mouth and long before his sexual assault trial started ... so says one of the jurors.

Harrison Snyder appeared on 'GMA' Monday and said the unimpeachable evidence that led to the comedian being found guilty beyond a reasonable doubt of drugging and molesting Andrea Constand in 2004 -- Cosby fessing up.

Snyder admitted he knew ZILCH about the mounting allegations against the comedian heading into the trial and didn't think it was "an open-and-shut" case. But, what sealed the disgraced comedian's fate was his own deposition.