When one of Oswald's superior officers in the Marines learned of his supposed role in the JFK assassination, he was shocked and disbelieved it because he thought that Oswald lacked the skill and training for such difficult shots.
Similarly, in 1987, former U.S. Marine Corps sniper Craig Roberts, a Vietnam war veteran, went to the 6th floor of the Texas School Book Depository and looked from the putative sniper position. He knew immediately that the Warren Commission's findings were implausible. Roberts regarded it as impossible that Oswald, acting alone, could have fired from that position three shots in 5.6 seconds with an old, obsolete, and poorly fitted bolt-action rifle.
Paraffin tests administered in Dallas soon after Oswald was arrested showed metallic residues associated with firing a gun on Oswald's hands but not on his cheek, even when subjected to a sophisticated analysis that required a nuclear reactor. The best explanation for this is contamination on Oswald's hands or that, as claimed, he fired his revolver and killed Officer Tippet.
No matter what Oswald's level of skill with a rifle was, the lack of metallic residues on Oswald's cheek is strong forensic evidence that he did not fire a rifle on the day of the assassination. Notably, it took a lawsuit to pry the negative results from the FBI, which had not forwarded the written report to the Warren Commission.