If writing is made on a piece of paper which is resting, either directly or indirectly, on another piece of paper then indented impressions of the writing will be created in the lower piece of paper. A typical example of this is in a pad of paper. There are numerous factors which can make the impressions more or less legible. Two obvious factors are the type of pen used and the number of pieces of paper between the top sheet and the sheet being examined. However, even when there are no impressions visible to the naked eye our sensitive techniques may be able to visualise them. In favourable situations we can detect indented impressions seven sheets below the original writing using ESDA.
Clues left by indentations
Indentations can be used forensically for a number of different purposes. They can provide intelligence information such as names, addresses, telephone numbers and email addresses which are not visible to the naked eye. If the source of the indented impressions is found (i.e. the top sheet) then they can show that those pieces of paper were in direct or indirect contact in the past thus linking them together. In more complex cases the order that writing and indentations were made may be deduced providing significant information regarding a sequence of events. For example an entry in an old diary may have been made much more recently than the date in the diary indicates in order to present a misleading scenario (e.g. to present an apparent alibi for a crime). Evidence of the sequence of entries may demonstrate that the entry has been made later than the surrounding entries.
Indented impressions can be visualised using ESDA, by oblique light (light shone at a shallow angle) or by creating a cast of the surface of the document. For normal paper ESDA is usually the preferred method as it is the most sensitive and provides a permanent 'lift' showing the indentations. However if the paper has been wetted (e.g. the document has been treated for fingerprints using ninhydrin) then ESDA won't work and one of the other methods will be required.