The first rule of patsies is, once you find one, you stop looking. That's how the police work every day.
That, and it's easy to paint over a complex conspiracy by calling the tip of the spear a 'nutter' and closing the case. I think we have seen a lot of that in the past decades, and anyone saying otherwise has been branded a "conspiracy theorist" (or worse) in order to make censoring them easier. Consider, though, that by forcing denial, many diabolical plans just may have been foiled.
