Exclusive Interview: Opto-Digital Microscopy Reveals Fingermarks on Metal in CSI (part one)

At the beginning of a forensic investigation, light microscopy is often the technique of choice as it is quick, accessible and most importantly non-destructive towards precious and irreplaceable samples. SelectScience's Dr Lois Manton-O'Byrne spoke with Dr Kevin Farrugia, of Abertay University, UK, about an opto-digital microscope that combines optical and digital technologies to enable the visualization of previously difficult samples. Dr Farrugia's main research focus includes the development of enhancement techniques for fingermarks and footwear marks, as well as the analysis of illicit drugs of abuse and ink.

Metal Surface Fingerprints
One of Dr Farrugia’s main focus areas is the detection of fingerprints or marks on metals at crime scenes. Criminals are often conscious to remove evidence, but latent prints on metals may prevent this from happening. "Once contact has been made, some of the chemicals in sweat can react with the metal and the fingerprint is effectively etched into the surface," says Dr Farrugia. "This leaves a permanent mark that no amount of wiping will remove. Where there is an attempt to remove the trace of contact with the metal surface, this can also suggest intent to remove evidence. Some techniques used for non-porous surfaces may also work on metals, such as cyanoacrylate (superglue) fuming; but there are also specialized techniques such as electrochromic enhancement."

Opto-Digital Microscopy
Once the fingerprint has been taken, it is analyzed with opto-digital microscopy. "Prior to powdering or using any other chemical technique, it is useful to use non-destructive techniques for visualization and recording,” says Dr Farrugia.

"At Abertay, the marks were heated to high temperatures above 400°C before capturing and analyzing images of the mark using the Olympus DSX100. Visualizing the complete print at higher magnification was important for in-depth analysis, and in all images this was enabled through the image stitching function of the DSX100. Although in some cases the detail generated from these prints may not be sufficient to provide an exact positive identification, they can also be used in conjunction with other information, or to rule out a suspect."

In a Court of Law
The evidence has now been collected, so it can be submitted to a court. "Microscopy and visualization is accepted by the British courts, and the DSX100 is not any different,” says Dr Farrugia. “The techniques mentioned here, such as powdering and powder suspensions, are recommended by the Home Office Fingermark Visualisation Manual, which is a respected, world-class document that every major police department in the world will have. The techniques discussed in the manual have been validated and shown to work under a certain standard, most notably ISO17025."

Image: Fingerprints were here visualized from copper wiped with wool using the Olympus DSX100. Images courtesy of K Dettori, Abertay University