Tape evidence from crime scenes
Tape evidence from crime scenes refers to various adhesive tapes that may be encountered by law enforcement during investigations. These tapes, commonly made from polymers or other materials, are significant in cases such as homicides, kidnappings, and drug trafficking. Forensic experts analyze tape samples by comparing their physical and chemical properties with those of control samples from suspects or other sources. The examination process includes assessing characteristics like color, texture, width, and thickness, as well as using advanced techniques such as spectroscopy and microscopy to determine chemical compositions.
Types of tapes frequently analyzed include packaging and electrical tape, with specific methods applied depending on the tape's material. A conclusive match between tape samples can be established through physical fits or similarities in manufacturing striations. In addition to identifying criminal activity, adhesive tapes also play a role in the collection of other evidence, such as fingerprints and biological samples, further emphasizing their importance in forensic investigations. Overall, tape evidence is a valuable tool for forensic scientists in unraveling the complexities of criminal cases.
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Tape evidence from crime scenes
DEFINITION: Manufactured product that consists of a long strip of a backing film with an adhesive applied to one side that allows the film to be stuck to a surface.
SIGNIFICANCE: Law-enforcement investigators may encounter various kinds of adhesive tapes as evidence in a range of cases, including homicides, kidnappings, drug trafficking cases, and cases involving explosive devices. By analyzing tape evidence recovered from crime scenes, comparing the physical and chemical properties of the samples with pieces or rolls of tape recovered from suspects or from other items, forensic scientists can provide investigators with valuable information.
Pressure-sensitive adhesive tapes are generally composed of several layers: a release coating, a backing film, and an adhesive coating. The release coating is a very thin layer that prevents the tape from sticking to itself when wound on a roll. The backing film is commonly a type of polymer, such as polyethylene, polypropylene, or polyvinyl chloride, but paper and cloth tapes are also available. The type of adhesive coating used depends on the specific application of the tape, with the most common types of adhesives being natural rubber, styrenated rubber, and acrylic polymers. Packaging tape and electrical tape are the most common types of tapes that forensic scientists encounter in their work.
The first stage of the examination of a tape evidence sample consists of a comparison of the physical characteristics of the recovered and control samples. This includes comparison of the color, surface texture, width, and thickness of the backing film and the adhesive layer. Optical properties such as birefringence and fluorescence are also compared for some tapes. The forensic scientist may use microspectrophotometry to compare the colors of the tapes objectively. Surface striations may also be visible on the film; these are imparted to the tape during its manufacture. Examination of these striations can be carried out in a way that is analogous to a tool-mark comparison.
A range of analytical techniques are then applied to the backing film and to the adhesive layer to determine their chemical compositions. The choice of techniques used depends on the instrumentation available. Techniques commonly applied include Fourier transform infrared (FTIR) spectroscopy, pyrolysis gas (PyGC), X-ray fluorescence (XRF), and scanning electron microscopy with (SEM-EDS). If cloth tapes are being examined, the fibers present in the tape are also analyzed.
A conclusive match of the recovered and control tape samples is possible if a physical fit is found between the fractured ends of the two samples. A correspondence of striations on the surface of the film may also prove a conclusive match if it can be shown that the marks alter during the manufacture of the particular tape being examined. Otherwise, a correspondence of physical and chemical features results in a match of class characteristics; the evidential value of such a class match is determined through reference to surveys of similar types of tapes.
The use of adhesive tape remained one of the main ways to collect evidence into the 2020s. Police investigators used fingerprint tape not only to collect fingerprints but also to collect dried blood stains that could then be transferred to a clear piece of acetate and sent to a lab. Water- or methanol-soluble tape could also be used to collect hair and fiber samples.
Bibliography
"Collection Techniques." National Institute of Justice, 15 June 2023, nij.ojp.gov/nij-hosted-online-training-courses/crime-scene-and-dna-basics-forensic-analysts/evidence-crime-scene/collection-techniques. Accessed 19 Aug. 2024.
Maynard, Philip, Katrina Gates, Claude Roux, and Chris Lennard. “Adhesive Tape Analysis: Establishing the Evidential Value of Specific Techniques.” Journal of Forensic Sciences 46, no. 2 (2001): 280-287.
Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 9th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007.