1. ”Suspect Documents, Their Scientific Examination” by Wilson R. Harrison, Published 1958 by Sweet and Maxwell Limited, Great Britain.
2. ”Questioned Documents” (Second Edition) by Albert S. Osborn, Published 1929 by Boyd Printing Company, Albany, New York, U.S.A.
3. ”Scientific Examination of Questioned Documents” (Revised Edition) by Ordway Hilton, Published 1982 by Elsevier North Holland Ine., New York, U.S.A.