The main character has 85 minutes of videotape that completely exonerates him. There is no way he could be convicted and sent to prison. Unless he lived in Arkansas, maybe.

the film might exonerate him, but that's beside the point. Subscribing to the argument that Ohlinger was telling the truth, the evidence that clears him is pointless. The powers-that-be wanted him silenced, wanted him incarcerated, and, taking this notion to its logical extreme, wanted him eliminated -- evidence be damned. The fact that he *was* convicted and murdered in prison (with no suspect ever found) further supports this theory.

The problem with your theory is that it is entirely contingent on Ohlinger having told the truth. If this is so, that completely eliminates any element of ambiguity in the film, which was its most interesting aspect. Without the ambiguity, the film is greatly lessened.

Also, you are disregarding the fact that the main character or his friend certainly would have gone public with his tapes. As a matter of fact, he must have gone public or else we would not be watching the movie in the first place!