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Research has demonstrated that impressions can be successfully visualized from documents up to 60 years old, provided the papers are not mishandled or stored improperly.Revealing indented writing using the electrostatic detection apparatus (ESDA) () Detecting alterations, obliterations, erasures and page substitutions ― Alterations, obliterations and erasures not visible to the human eye can often be detected through use of photography and other imaging devices that utilize ultraviolet and infrared wavelengths of light.In cases involving handwriting, samples are usually divided into two types: requested writing specimens and collected writing specimens.Requested specimens are writings dictated by the investigator to the writer.The techniques and tools used in forensic document examinations leverage well-established principles of physics and chemistry.A typical Questioned Documents unit in a crime laboratory is equipped with microscopes, digital imaging instrumentation, infrared and ultraviolet light sources, video analysis tools and specialized equipment including electrostatic detection devices (EDD) and materials to perform analytical chemistry.
In some circumstances, graffiti and digital signatures may be examined; however, the client should be aware that the examination of these types of evidence can be problematic.Good sources of writing specimens may include items such as cancelled checks, letters, diaries, signed receipts, medical records, real estate contracts, tax records or other signed legal documents.The analysis should be performed by a qualified forensic document examiner, preferably one who is a member of a well-established professional association such as the American Board of Forensic Document Examiners (ABFDE) or the American Society of Questioned Document Examiners (ASQDE).(Courtesy of Marie Durina) Determining individual dye components ― An examination called liquid chromatography can be conducted to identify the chemical composition of inks on a document.
In this technique, a small cutting from the questioned document is dissolved in a solvent and analyzed.
This causes the toner used in the EDD to be attracted to these areas, revealing indentations that are present.