Visualization of latent fingerprints beneath opaque electrical tapes by optical coherence tomography

Electrical tape is found as one type of important trace evidence in crime scene. For example, it is very frequently used to insulate wires in explosive devices in many criminal cases. The fingerprints of the suspects were often left on the adhesive side of the tapes, which can provide very useful clues for the investigation and make it possible for individual identification. The most commonly used method to detect and visualize those latent fingerprints is to peel off each layer of the tapes first and then adopt the chemical methods to develop the fingerprints on the tapes. However, the peeling-off and chemical development process would degrade and contaminate the fingerprints and thus adversely affect the accuracy of identification. Optical coherence tomography (OCT) is a novel forensic imaging modality based on lowcoherence interferometry, which has the advantages of non-destruction, micrometer-level high resolution and crosssectional imaging. In this study, a fiber-based spectral-domain OCT (SD-OCT) system with ~6μm resolution was employed to obtain the image of fingerprint sandwiched between two opaque electrical tapes without any pre-processing procedure like peeling-off. Three-dimensional (3D) OCT reconstruction was performed and the subsurface image was produced to visualize the latent fingerprints. The results demonstrate that OCT is a promising tool for recovering the latent fingerprints hidden beneath opaque electrical tape non-destructively and rapidly.