There is no conspiracy. Just twelve people dead.
Alan J. Pakula's The Parallax View, a superb conspiracy thriller about one man's paranoia that turns out to be total, incredible fact, ranks among the best movies of its kind.
Warren Beatty is a news reporter who, aong with seven others, witnesses the assassination of a political candidate. When the other seven die in "accidents", the newsman begins to doubt the offiical position: that the lone madman was responsible for the crime. He imagines a sophisticated network of highly trained murderers. But his nightmares pale against the bizarre truth he uncovers.