Semester

Summer

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Tatiana Trejos

Committee Co-Chair

Ruthmara Corzo

Committee Member

Ruthmara Corzo

Committee Member

Tina Moroose

Committee Member

Casper Venter

Abstract

Tape evidence is often used in criminal cases involving violent crimes, kidnappings, improvised explosive devices (IEDs), and drug trafficking. This evidence can reveal potential links between suspects, items, or scenes. The forensic examination of electrical tape can provide investigative leads or offer support to alternative hypotheses evaluated in the courtroom. A conventional analytical scheme includes microscopic examination, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy Energy Dispersive Spectrometry (SEM-EDS), and Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC/MS). Elemental analysis of electrical tapes is commonly achieved using SEM-EDS; however, recent scientific literature suggests that this analysis can evolve from using SEM-EDS to more sensitive and informative methods such as Laser-Induced Breakdown Spectroscopy (LIBS), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), or micro-X-ray Fluorescence Spectrometry (µ-XRF). Recent advances in μ-XRF technology that use silicon drift detectors (SDDs) provide superior sensitivity and precision while being already adopted by public laboratories for other trace materials. This study aims to offer foundations to expand the use of µ-XRF for tape evidence, making the use of the technique at trace laboratories more cost-effective.

In addition to the clues that the tape itself can provide during a criminal investigation, its backing and adhesive layers are a potential substrate for other traces, such as fingerprints. Therefore, it is of interest for forensic laboratories to be capable of examining relevant interconnected evidence that may appear on a singular tape specimen without risking the integrity of the evidence. Information on how chemical tape examinations can be affected by fingerprint development or vice versa is lacking. In this study, we investigate recommendations for preserving these types of evidence when both fingerprint and tape comparisons are required.

This study evaluates the optimal workflow to incorporate µ-XRF in electrical tape examinations, and the interpretation of chemical data when the tape needs to undergo latent fingerprint development. The dataset consists of contemporary electrical tape samples from 45 rolls produced in four countries, from seven manufacturers, ten brands, and various quality grades (high, medium, low); ten sections are sampled per roll. Pairwise comparisons (990) evaluate between-source discrimination and false inclusions. The set also contains five rolls with 20 sections per roll. Pairwise comparisons (950) are conducted between sections of each same-source roll to evaluate within-source variability and false exclusions. Samples are examined by physical and microscopic analysis, ATR-FTIR spectroscopy, µ-XRF with an SDD, and Py-GC/MS. Performance rates are reported for each technique alone and combined. The µ-XRF spectral data is also evaluated under conventional spectral overlay approaches and quantitative metrics (spectral contrast angle ratio; SCAR) that assess the similarity or dissimilarity of the spectra. Due to high discrimination and classification, it is recommended that µ-XRF analysis moves to the forefront of the analytical scheme to optimize turnaround times, costs, and resources. The study also shows how chemical tape examination is affected by fingerprint development or vice versa and provides recommendations for proper sample handling in the latent print and trace evidence units.

Finally, an interlaboratory study evaluates inter-examiner and inter-instrumental variability and assesses the relative informing power of µ-XRF analysis of electrical tapes. A novel spectral similarity metric (SCAR) provides a more objective comparison and interpretation of the data, while minimizing inter-instrumental variability. The test consists of ten sets of electrical tape samples from various ground truth sources (same roll, same package, different rolls), each one with five sections per set. The data is collected across eight laboratories, representing 11 instrumental configurations. The results from pairwise comparisons using spectral overlay and SCAR (45 each) are compared for each laboratory (8) and instrumental parameters (11). The results of this study indicate a strong agreement between laboratories, with low false exclusion and inclusion rates. This information can be used to identify relevant parameters for consistent analysis and interpretation across different laboratories. This knowledge will extend the value of pressure-sensitive tape as evidence to further substantiate case results in the courtroom and during investigative stages.

Embargo Reason

Publication Pending

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Available for download on Wednesday, June 11, 2025

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