Improving forensic casework analysis and interpretation of gunshot residue (GSR) evidence
- Publication Type:
- Thesis
- Issue Date:
- 2011
Open Access
Copyright Clearance Process
- Recently Added
- In Progress
- Open Access
This item is open access.
There are two main challenges to gunshot residue (GSR) evidence.
The first concerns analysis. The lack of screening techniques complicates sampling and
analysis of large areas or numbers of exhibits. Also, lead or heavy metal free
ammunitions present limitations to the technique for confirmatory detection of residues
- scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX).
A screening technique was developed to detect GSR components from all ammunition
types. Ion mobility spectrometry (IMS) was proven to allow sensitive and effective
screening before proceeding to confirmatory analysis.
Lead and heavy metal free ammunitions were examined and a technique developed for
detecting components in the organic portion of the residue. Liquid chromatography
tandem mass spectrometry (LC-MS/MS) was extremely effective, detecting twenty
seven components. The technique is sensitive (to around 1 ppb ), selective, rapid and
cost effective. The combination of IMS, SEM/EDX and LC-MS/MS, with visual,
physica] and microscopic examination, is proposed as a complete protocol for GSR
analysis from all ammunition types.
The second challenge involves interpretation. Factors that lead to positive and negative
findings must be considered and the weight of evidence assessed. Both background data
and application of an interpretive framework have been inadequate.
Background levels of GSR in the NSW general population and NSW Police Force were
studied and the chances of random presence on a suspect and of contamination during
arrest and sampling process determined.
Nil GSR was detected on hands of the NSW general population or the sample of general
duties police officers. A moderate probability was demonstrated for low levels of GSR
on hands of crime scene investigators. GSR was detected on hands of all forensic
firearms examiners tested, however their role limits access to suspects and items
sampled for GSR, limiting the chance of contamination. Significantly, one high risk
area for contamination was identified, the tactical response officers.
Background levels of GSR in the Australian Federal Police laboratories were compared
before and after implementing contamination controls. The configuration of the original
laboratory along with the lack of controls lead to GSR being detected on almost every
sample. The newer laboratory was extremely clean, only one GSR particle being
detected, demonstrating the importance of effective contamination controls during
sample collection and analysis.
A statistical interpretive framework was developed. The model utilises Bayesian
networks to consider existing data relating to transfer and persistence, and new data
from this research, providing more objective assessment and allowing broader
application of the Bayesian framework.
Please use this identifier to cite or link to this item: