In a document filed Wednesday, FBI officials say they found the material on a computer seized last week from the Annapolis, Md., apartment where 88-year-old James von Brunn lived.
The FBI said in separate documents it found dozens of rounds of .22-caliber ammunition in a search of von Brunn's car. They also found business cards advertising a Web site that claims the Navy's USS Liberty was "brutally attacked" by Israeli forces in 1967.
Von Brunn faces murder charges in the guard's death. Authorities say von Brunn's car was parked outside of the Washington, D.C., museum during last week's shooting.