Foundations of Forensic Document Analysis by Allen Michael J.;

Author:Allen, Michael J.; [Allen, Michael J.]
Language: eng
Format: epub
Publisher: John Wiley & Sons, Incorporated
Published: 2015-09-28T00:00:00+00:00

Figure 4.14 Letter e printed with a laser printer showing the molten appearance of raised toner on a paper surface (x30 approx.).

The cylindrical drum can, with use, develop small imperfections on its surface. These imperfections may attract toner particles such that each time documents are printed using it there will be a characteristic mark on the paper. The position and shape of such marks can provide forensic evidence linking documents printed using the same laser printer (specifically the drum) or linking documents to a particular printer. The drum marks are often very small and require low power magnification to be seen.

Given the likelihood of a background scatter of toner particles on a document, it is important to distinguish them from marks caused by drum defects. A difference between them is that background scatter is random whereas drum marks will appear repeatedly on documents, usually in the same relative position one to another on the document. The diameter of many laser printer drums is quite small such that to print a sheet of A4 paper requires perhaps three rotations of the drum. This will cause the drum mark to appear three times down the page spaced equally apart. Background scatter usually consists of one or a few toner particles, whereas drum marks often have a shape associated with them (Figure 4.15). Any shape to drum marks will add to their forensic significance.

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