The theories expressed in the film are really a combined jumble of Garrison's and Jim Marrs, who wrote Crossfire, and bear very little relation to each other.

Garrisson's ideas - or at least his primary theories - have been pretty much debunked by assassination researchers over the years, altho there are, I believe,a few kernels of interest and truth in them (David Ferrie, for example).

Stone, I think, took some of the plausible elements of both and combined them, which is one of the main criticisms of the film - it's accuracy with respect to the facts and theories.

I personally believe, however - and always have - that there definitely was a conspiracy - government sponsored, or at least government covered-up to some degree - behind the JFK assassination.