On the reliability of the forensic examination of electrical tapes and the influence of alteration sources encountered in casework

Pressure-sensitive tapes are routinely submitted to forensic laboratories due to their wide use in a variety of crimes such as kidnapping and terroristic attacks involving the use of explosives. Particularly, electrical tapes are often used in the fabrication of explosive devices. Hence, their ubiquity and special uses in certain categories of grave crimes make them important types of physical evidence where forensic findings can contribute significantly to developing investigative leads and evaluating associations between unknown-origin tapes and suspected sources. However, tape specimens recovered in casework are seldom in pristine conditions and examiners must deal with the influence of various environmental or anthropogenic effects that may degrade or alter the chemical components of the tape. Typical sources of alterations are post-blast effects, previous latent print processing, and weather conditions.

    Addressing multiple research needs developed by the OSAC Trace Materials Subcommittee, the American Society of Trace Evidence Examiners (ASTEE), and the NIJ Technology Working Group (NIJ-TWG), this project aims to establish a comprehensive reference collection representative of the current market consisting of 160 electrical tape samples of 10 colors and different end-uses by characterizing them with analytical methods routinely used in trace evidence examinations for tape, including attenuated total reflectance Fourier transform infrared (ATRFTIR) spectroscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), pyrolysis gas chromatography-mass spectrometry (py-GC-MS), and the novel method of direct analysis in real-time-mass spectrometry (DART-MS). More importantly, this study investigates various casework relevant alteration sources including post-blast effects following explosions initiated with TNT and PETN, latent print development using routine methods of cyanoacrylate fuming, powder suspension (i.e., Wetwop), and fingerprint powders, as well as environmental conditions of outdoors sunlight exposure and water immersion.

    This project is divided into two distinct phases which both include data acquisition and data analysis. The first includes the analysis of pristine samples, while the second involves the analysis of tapes exposed to the various sources of alterations. Data analysis aims to identify the chemical components of electrical tape, to study complementarities and redundancies between the different methods within the established analytical scheme and the novel DART-MS, and to use chemometric approaches and multivariate statistical tests to address the effects of the different alteration sources.

    This study is expected to significantly improve the reliability of forensic tape examinations in producing investigative leads and enhance the confidence of examiners during comparisons, especially in the multitude of cases where recovered tape specimens are not in pristine conditions. CA/NCF