Many Conspiracy Theorists have said that the Warren Commission started with the belief that Oswald alone was guilty and that the Hoover FBI then proceeded to withhold, alter and destroy evidence and twist the words of witnesses to attain that result.
All true! But Oswald alone *was* guilty. And the Hoover FBI had valid reasons for doing what they did.
in The Final Truth:
Solving the Mystery of the JFK Assassination: