An investigation into secondary transfer of trace DNA to evidentiary items via nitrile gloves during crime scene examination

Author

Molly G. Younker, West Virginia UniversityFollow

Semester

Spring

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Forensic and Investigative Science

Committee Chair

Arati Iyengar

Committee Member

Amy Welsh

Committee Member

Tina Moroose

Abstract

An investigation into secondary transfer of trace DNA to evidentiary items via nitrile gloves during crime scene examination

Molly G. Younker, B.S.

The introduction of highly sensitive DNA profiling kits has led to an increase in success with samples containing sub-nanogram amounts of DNA such as touched or handled objects including doorknobs, tools, steering wheels, etc. Such trace DNA is easily transferred between individuals and objects. Studies have shown that in addition to primary transfer due to direct contact, trace DNA can also be indirectly transferred in secondary and tertiary transfer steps which do not require direct contact. Nitrile gloves worn by investigators at crime scenes can be high risk vectors for secondary transfer and investigator-mediated contamination. This can be detrimental to the interpretation of evidence and can lead to incorrect associations between the profile obtained and the crime event itself. We examined the prevalence of secondary transfer of trace DNA via nitrile gloves worn by examiners during mock crime scene examinations. Using human volunteers who acted as ‘Perpetrator’, ‘Innocent Person’ or ‘Examiner’, for each simulation, we got an ‘Innocent Person’ to touch one of three commonly encountered target surfaces (door handle, door edge, or light switch) followed by the ‘Examiner’ touching one of the surfaces while wearing nitrile gloves and subsequently collecting and packaging an evidence item (screwdriver or rope) left behind by a ‘Perpetrator’. Each simulation was performed in triplicate for each target surface and using six innocent persons per evidence item for a total of 108 simulations. Swabs were taken of the glove, evidence item, and surface from each simulation. DNA was extracted, quantified, and amplified using the GlobalFiler™ kit. Profiles generated were compared to reference profiles to determine the number of unique transferred ‘Innocent Person’ alleles, number of shared alleles between the ‘Innocent Person’ and the ‘Perpetrator’, and number of unique ‘Perpetrator’ alleles. We observed alleles unique to the ‘Innocent Person’ on the evidentiary item in 51% (55/108) of the simulations, with up to 13 in a single sample. We also estimated Likelihood Ratios (LRs) for the ‘Innocent Person’ being included as a contributor to the mixed DNA profile recovered from the evidence item using EuroForMix v. 4.0.7. Although the vast majority of LRs were (64/82), we obtained high LRs of 1221, 6.1 x 10⁷, and 1.5 x 10⁸ in three simulations, highlighting that nitrile gloves pose a high risk for DNA transfer and reinforcing the importance of proper training for investigators and the need for frequent and strategic glove changes during examinations.

Recommended Citation

Younker, Molly G., "An investigation into secondary transfer of trace DNA to evidentiary items via nitrile gloves during crime scene examination" (2024). Graduate Theses, Dissertations, and Problem Reports. 12366.
https://researchrepository.wvu.edu/etd/12366

Embargo Reason

Publication Pending