FBI Director J. Edgar Hoover lied to the Warren Commission, claiming (in a single un-sworn letter) that the spectrographic analysis of the bullet gouge in the Main St. curb showed no copper. If the test had supported Hoover’s claim, the FBI would have released the results immediately. Instead they destroyed them.
This was just part of the FBI cover-up. The Final Truth explains why Hoover lied about this and the reasons behind the cover-up.
The Final Truth: Solving the Mystery of the JFK Assassination
Paperback or Kindle: http://www.amazon.com/gp/product/1490350578