Imaging the time sequence of latent electrostatic fingerprints

Biometric identification for forensic investigations and security continues to depend on classic fingerprinting in many instances. Existing techniques rely on either visible deposits or hidden (latent) fingerprints resulting from the transfer of residues from the finger to the surface. However, one of the limitations of classic fingerprinting, for use as forensic evidence, is in determining a time sequence of events. It is extremely difficult to establish a timeline, from fingerprint evidence alone. We present the capability of a new technique which images the electrical charge deposited by tribocharging when a finger contacts an electrically insulated surface. The method is applicable to insulating surfaces and has been tested on PVC, PTFE, Acetate and PVDF sheets. The latent electrostatic charge pattern is detected using a novel, microscopic, electric potential sensor. The sensor is capable of imaging static charge distributions non-invasively, with no discharging effect on the sample. We present data showing the decay of the charge image with time, over a period up to 14 days. This capability has two major implications. First this technique does not suffer from ambiguities caused by a history of old fingerprints and second it has the potential to allow the time sequence of recent charge fingerprint images to be determined. © 2010 SPIE