Electrostatic detection device

An electrostatic detection device, or EDD, is a specialized piece of equipment commonly used in questioned document examination to reveal indentations or impressions in paper that may otherwise go unnoticed.

EDD equipment and investigative techniques were central to overturning a number of convictions in the United Kingdom, as it was possible to demonstrate that witness statements had been altered or signed as blank pages in reverse order to the main notes.

In some situations, a questioned document such as a ransom note, or an extortion letter, may exist which can be determined to be the source of indentations detected on another piece of paper (e.g., an offender's notepad).

For example, an anonymous letter may bear impressions of writing that relate to some mundane activity of the offender which could ultimately lead an investigator to a particular suspect.

Rather, Seward in 1998[5] and 1999[6] proposed an alternative theory explaining the detection capability of an EDD as being due to a surface charge effect created by paper-to-paper friction specifically in the area where a writing instrument is pressed down into the top-most sheet of paper.