Jean Hill, a teacher who says she witnessed shots fired from the grassy knoll, tells the investigators that Secret Service threatened her into saying three shots came from the book depository, revealing changes that were made to her testimony by the Warren Commission. Garrison's staff also test the single-bullet theory by aiming an empty rifle from the window through which Oswald was alleged to have shot Kennedy. They conclude that Oswald was too poor a marksman to make the shots, indicating someone else, or multiple marksmen, were involved.