Date of Submission

5-2024

Document Type

Thesis

Degree Name

Master of Science in Forensic Science

Department

Forensic Science

Advisor

Ted Schwartz, M.S.

Committee Member

Alyssa L. M. Marsico, Ph.D.

Committee Member

Daniel Rothenberg, M.S.

Keywords

Crime Scene Investigations, Human Hair, Trace Evidence, Somatic Origin Analysis, Amino Acid

MeSH

Hair, Amino Acids

LCSH

Hair--Analysis, Trace evidence, Amino acids, Crime scene searches

Abstract

In crime scene investigations, human hairs are some of the most common pieces of trace evidence encountered. When hairs are analyzed, somatic origin analysis is often overlooked, thereby bypassing crucial contextual information. Pubic hairs may be probative evidence in a sexual assault while limb hairs may be important in a stabbing. Current somatic origin analysis is dependent on microscopic examination, particularly rooted in characteristics typically perceived as indicative of a certain body location. However, there are complications with overlapping characteristics or lack of typical characteristics in transitional areas of the body. Thus, somatic origin analysis should not rely solely on microscopy, and there are currently no DNA procedures that are helpful. Proteins, on the other hand, are much more robust and provide a possible solution to somatic origin determination. Non-synonymous amino acid changes in the protein sequence cause single nucleotide polymorphism profiles that can differentiate individuals. These changes can be exploited as additional approaches to hair analysis. Proteomic techniques have been heavily researched for the use of genetically variant peptides (GVPs) as a differentiating factor between individuals. Amino acid studies can build upon the approach used by proteomic studies. Recent studies have demonstrated the use of amino acid quantities in differentiating between individuals based on general class characteristics such as age group, geographical origin, and sex. Macri et al. successfully showed that different amino acid ratios of two individuals with morphologically similar hairs were able to differentiate between them. A study conducted by Yaroshuk demonstrated the possibility of amino acid ratios being used as an exculpatory method. Expanding on concepts from these studies, this thesis evaluated the potential of using amino acid analysis in conjunction with microscopy to differentiate between hairs of different somatic origins. This study included 97 samples from 9 somatic origins collected from 17 consenting participants. Methodology of hair analysis combined microscopy and gas chromatography-mass spectrometry to obtain amino acid quantities.

Microscopic analysis revealed that the characteristics we rely on for somatic origin identification are not as reliable as previously thought. Of the approximate 450 pubic hairs examined, only 22 buckles were observed (~4.5%) with additional buckles observed in beard, chest, and scalp hair samples. These results indicate that buckling is not only observed at a much lower frequency than previously thought, but it is not exclusive to pubic hairs. Morphometric data analysis also supports the fact that no single characteristic is sufficient for somatic origin identification; however, the additive effects of various characteristics may increase discrimination for making a somatic origin determination.

Amino acid ratios were calculated for each somatic origin and data analysis was conducted to identify any unique significant differences in amino acid ratios that can be used to differentiate among somatic origin of hairs. Promising amino acids ratios were identified; however, further research is encouraged to evaluate their potential for application in differentiating somatic origin of hairs.

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