O'Brien offers a brief history of the uses of analysis of handwriting and printed documents followed by his best-chosen reference case: the New York Zodiac Killer. O'Brien mentions notes written by the Zodiac Killer, but does not detail the full role the letters played in the case. “For years the Zodiac has been provoking the police with strange codes, phone calls, offensive and cryptic messages. . . . [A cipher key] was handwritten on a blank sheet of paper and was accompanied by a short typed note on a 3x5 index card expressing the hope that "the enclosed key will prove advantageous to you in relation to the writer of the cipher letter." It was signed "concerned citizen" (crimelibrary.com). Providing full details supports Holmes' approach of using documents (written and typed) as well as the case containing the