Principles of Forensic Document Examination
Forensic document examiners often deal with questions of document authenticity. To determine whether a document is genuine, an examiner may attempt to confirm who created the document, determine the timeframe in which it was created, identify the materials used in its preparation or uncover modifications to the original text.
Documents can be examined for evidence of alterations, obliterations, erasures and page substitutions. Or the examiner can study the methods, materials or machines that created the document, providing key information that can identify or narrow the possible sources of the document. The ink, paper, writing tools, ribbons, stamps and seals used in production of the document may all reveal important clues. The examiner may even discover valuable evidence in a document’s invisible impressions.
A key element of document examination focuses on handwriting. Forensic examination and comparison of handwriting, which includes hand printing and signatures, is based on three main principles: (1) Given a sufficient amount of handwriting, no two skilled writers exhibit identical handwriting features; (2) every person has a range of natural variation to his or her writing; (3) no writer can exceed his or her skill level (i.e., it would not be possible for a marginally literate person who has only learned to produce very basic hand-printed letters to execute perfectly formed, highly skilled cursive writing).
Computer databases maintained by the U.S. Secret Service, German Federal Police and Federal Bureau of Investigation contain handwriting samples from hundreds of thousands of writers. Comparisons of these databases have not identified two individuals who have the exact same combination of handwriting characteristics, adding to the authenticity of handwriting as a solid form of evidence.