Technique Suggests Adding UV/IR Photography to Fingerprint Retrieval Process
Written By: Frederick Zigan
*This article was originally published in Forensic Magazine in June 2020 When recovering identifiable friction ridge patterns from semi-porous materials, such as retail packaging like cereal boxes, band aid boxes and other items that have printed multi-colored surfaces on one side and a paper backing on the other, most investigators default to magnetic powder. Others attempt cyanoacrylate fuming with a dye stain. Unfortunately, the latter can result in the distortion of the pattern by applying a liquid to the substrate, or the actual destruction of the evidence. This article suggests that the integration of a full spectrum camera into the sequence of processing this type of evidence offers a valuable first look--before performing a process that could potentially alter or destroy it.
Deciding how to process evidence when looking to retrieve identifiable friction ridge patterns can be difficult at times. However, the philosophy of starting with the least destructive method and working toward the more destructive method can never change. Also, photographing the evidence during each sequence of these steps is paramount in case the next is too destructive. During the research of this project, a collection of forensic practitioners from varying agencies were asked what their “go-to method” was for producing identifiable friction ridge patterns when working with semi-porous materials that had a multicolored or patterned background, such as lottery ticket scratch offs, band aid boxes, magazines, or certain retail packaging. The average response of approach method from those solicited was mostly the same with a few different variances. Some stated that they went straight to magnetic powder. Others lightly fume (cyanoacrylate) the item, then use magnetic powder and/or a combination of fluorescent powder then magnetic powder. There were others that used a method of cyanoacrylate fuming, then dye stained with MBD or Rhodamine 6G, applying with a pipette.
What was surmised was that after the fuming of the evidence, the first step utilized was to look at the evidence with oblique lighting to try and locate the friction ridge patterns. If patterns were found, they photographed under oblique lighting conditions and then proceeded to their next step, which was the application of some type of powder or dye stain. As stated before, applying liquid dye stains can alter or destroy the evidence when working with semi-porous substrates. Also, applying a powder, whether it is fluorescent, UV/IR, or magnetic powder, can still fill in some of the third-level detail, such as pores and edge shapes.
The combination of photographing the evidence with a full spectrum camera utilizing its ultra violet and infrared capabilities before these potentially destructive steps has been proven to be successful. During validation of this technique, the following materials were used: Fuji X-T1 UV/IR Mirrorless Full Spectrum Camera; Fuji Fujifilm XF 60mm f2.4 Fujinon Macro ASPH Super EBC Lens; B+W 39mm 403nm ultraviolet filter; B+W 39mm 830nm infrared filter; Misonix CA-3000 cyanoacrylate fuming chamber; UVFT100A ForensiTORCH from the megaMAXX 3-Watt Alternate Light System; Streamlight Stylus Pro (handheld white LED flashlight); Magnetic Fingerprint Powder – Sirchie (Regular Black).
The first thought that comes to mind is the addition to time to the processing sequence. The good news about the Fuji X-T1 UV/IR Mirrorless Full Spectrum Camera is that its live view is how the picture is going to turn out. What you see is what you get. This is beneficial because one does not have to take a photograph to see what is being seen by the camera. This feature enables the technician to essentially use the camera to scan the substrate looking for friction ridge patterns. To demonstrate this method, multiple fingers were rubbed on the forehead to apply a matrix of sebaceous oils. Multiple friction ridge patterns were deposited on the following: Band Aid box and a Toshiba hard drive retail packaging box pulled from the trash can of an office. The patterns that were deposited were intentionally applied to areas that had multiple colored or patterned backgrounds. All items were then fumed via the cyanoacrylate fuming method, in a Misonix automated fuming chamber, with a 20-minute fume time and 10-minute purge cycle. The processing sequence used in this method: the items were then removed from the chamber and viewed with a white light at oblique angles to locate potential evidence of friction ridge patterns. Once located, the patterns were photographed under normal light conditions, and again with oblique lighting. The recovered patterns were then photographed using a 403 nm filter and a handheld UV Light (365 nm). Magnetic powder was then applied to those same patterns and again photographed under normal light conditions. The author is aware that UV/IR powders could be introduced at this stage, however, magnetic powder was used as it is more prevalent. The patterns that now had magnetic powder applied were then photographed with an 830 nm filter, and fluorescent LED lighting from the ceiling of the lab.
An example of the results from the Band Aid box can be seen in Figure 1. In Figure 1(a) no friction ridges are observable and are barely observable using the oblique lighting in Figure 1(b). In figure 1(c) when using the UV filter, many more ridges are observed. Once the magnetic powder is applied, the fiction ridge pattern become more pronounced in Figure 1(d) and finally, most of the noise from the inks in the substrate are now a non-issue.
Figure 1: After fuming, the items were viewed via (a) normal lighting conditions, (b) oblique lighting, (c) a 403nm filter with 365nm UV lighting, (d) magnetic powder, (e) and finally with an 830nm filter with fluorescent lighting.
An example of how certain inks in packaging that work better with the 403nm filter and a handheld UV light (365nm) is Figure 2(c). The closest runner up in this series is Figure 5(b) where only oblique lighting is used.
Figure 2: After fuming, the items were viewed via (a) normal lighting conditions, (b) oblique lighting, (c) a 403nm filter with 365nm UV lighting, (d) magnetic powder, (e) and finally with an 830nm filter with fluorescent lighting.
The results show that with any piece of evidence, there is going to be multiple variables. The different colored or patterned backgrounds are made out of different materials. Products that are printed vary, and different types of inks are used that respond differently with a UV filter, and then differently with an infrared filter. Sometimes neither the UV filter, nor the infrared filter, perform; and something as simple as magnetic powder works best. But if you are left with just the magnetic powder, after photographing, your next step is to lift the friction ridge pattern. If tape is used, that could present problems such as bubbles, creases, and pulling part of the substrate off. Integrating the use of a full spectrum camera with UV/IR capabilities into the everyday sequence of processing semi-porous materials should be compulsory if the equipment is available. Photographing each step taken during processing should already be common practice or protocol. The time taken when changing the lighting conditions and filters is negligible when compared to the results. It is a non-invasive step that should not be bypassed if the equipment is readily accessible. Applying these small extra steps could aid in the recovery of far more identifiable friction ridge patterns.
Frederick Zigan is an associate team member at Delta-5 Labs, for more information check out his bio or his company National Forensics and Polygraph (www.national-forensics.com).