Comparative Analysis of Duct Tape

Duct tape is a common item that you can find in any toolbox or residence since its invention as a waterproof tape in the 1930’s. During World War II, duct tape was used by allied forces for various purposes and after the war it was used in homes for duct work, hence it’s commonly known name…”duct tape”. It is known for its very distinctive silver polyethylene backing but it can be now found in decorative colors. I recently have seen it in patterns ranging from camouflage to American university school logos.

It is found in vehicles, homes, and the DIY toolboxes and used for emergency repairs. Thus the easy accessibility of duct tape can be used by criminals as an evidential component to commit crimes. In homicides, a killer may use duct tape to tie the victim up or seal their body in some type of container. In rapes, the offender may also bound the victim and in hit-and-run homicides it can be used to reattach a damaged bumper. In terrorist attacks it can be used in energetic material construction (A.K.A. “bombs”). In other crimes it may be used to wrap around the handle of a sawed off shotgun to prevent wood splintering or used to wrap around a tool left at a crime scene. Arguably, the possibilities are endless to the usage and only limited by the criminal’s imagination.

Before we begin it is critical that readers understand a basic forensic theory of evidence, the Locard’s Principle. Dr. Locard (13 December 1877 – 4 May 1966) was known as the French version of the fictional character “Sherlock Holmes” laying the groundwork for the concept that every criminal leaves some type of trace evidence at a crime scene. Dr. Locard’s Priniciple is the basis for the scientific concepts of forensics and trace evidence. So, in descriptive terms---two offenders in a physical struggle will exchange trace evidence from the clothing they are wearing, transfer blood, transfer skin cells, transfer sweat, etc. This can also include the soil found on the bottom of an offenders boot to the exchange of DNA through skin to skin contact (notably forensics is making advances in “touch DNA” extracting DNA from skin cells left from touch---but there is much scientific improvement to be made).

In respect to duct tape, according to Locard’s Principle, the offender may leave his/her blood, hair, clothing fibers, his/her pet’s hair, etc. on the adhesive size of the duct tape. On the polyethylene backing, the offender may leave a latent fingerprint (see my previous blog post) or his/her DNA. Excluding obvious potentials for trace evidence recovery, the debate over duct tape has spawned from the idea that all commercially made duct tape can be traced back to an original manufacturing site which may be traced to a particular store in an area which might be further traced back to a purchaser of said duct tape linking it to a potential suspect. This is called fracture matching in comparative analysis of duct tape.

This concept of fracture matching of tape in forensic science began with Agron and Schecter’s (1986) study of electrical tape were they used photographic examination of two methods of tearing: tension and shearing, and determined that each tear was “unique and nonreproducible”. Their theory rests on the notion that each fracture of tape results in individual and unique characteristics resulting in a matching counterpart, with a matching end piece that holds high evidentiary value.

In the case of duct tape, shearing between two pieces occurs when the elastometric and fibrous materials of the polyethylene backing and the scrim fails. Duct-tape construction consists of a polyisoprene-based adhesive, fabric reinforcement (scrim), and a polyethylene backing (Johnston and Serra 2005). So in other words, the scrim, the component of duct tape that is woven or gauze-like of cotton or polyester blends is used to strengthen the tape. The scrim comprises of yarn running the length of the tape in the manufacturing machine direction which is known as the warp, while the yarn running across the tape is known as the fill (McCabe, Tulleners, Braun, Currie, and Gorecho 2013). The warp and the fill can vary based on the size, type of yarn, etc. based on manufacturing production---similar to the process of the manufacturing of sheets and bedding materials. The second piece of duct tape that holds evidentiary value is the outer adhesive which is manufacture specific and comprises of a combination of various elastomers, tackifying resins, and fillers (McCabe, Tulleners, Braun, Currie, and Gorecho 2013).

In 2007, the FBI discovered through research that relaying on backing analysis (the outer adhesive of duct tape) that…”identifying the tape manufacture in order to direct investigators toward a likely origin for duct tape evidence may not be possible solely by backing analysis” (Hobbs, Gauntt, Keagy, Lowe, and Ward 2007). So…in order for there to be any probability of any evidence of high evidentiary value the area of duct tape that should be examined is the fabric reinforcement area, the scrim.

Tulleners and Braun (2011) examined 1800 pieces of torn tape specimens and 400 cut tape specimens. They discovered that it is possible to match ends of duct tape to their origin 98.25 to 100 percent for torn tape and 98.15 to 99.83 percent for cut tape. So, Tulleners and Braun (2011) were able to determine that you can match a piece of tape to its connecting tape roll. In theory, a piece of duct tape could be connected to a manufacturing point--to a distributor---to a buyer---then potentionally to a suspect.

While what I like to call “manufacturing forensics” is a fairly new area of forensic science, its forensic evidentiary probability and usage should not be discounted. Based on the limited scientific research on fracturing matching of duct tape, more research should be done on the topic. In time, I believe that "manufacturing forensics" could be the future of fruitful evidence recovery by using the same concepts in other manufactured materials that are left at crime scenes. (Examples: clothing, footwear, medical tape, etc.)