While working on his Ph.D. thesis (from the late 1980s into the 1990s), Cristol analyzed the official investigations of the USS "Liberty" incident of June 8, 1967, in which Israeli forces attacked an American ship, resulting in a significant loss of life. Officially, the "Liberty" incident had already been investigated by more than a dozen government agencies and government-commissioned groups; it had always been reported to have been a tragic accident. Cristol conducted over 450 interviews. Freedom of Information Act requests were used to obtain declassification of the Clark Clifford Report, 22 hot-line messages, 22 National Security Agency documents, and 31 National Security Council documents. Cristol was also able to obtain classified Israeli documents. The conclusion of his dissertation confirmed the official investigations and demonstrated that the attack on the USS "Liberty" was a mistake.