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Impact of Submersion DNA Extraction on Firearms Examination

Retrospective pilot study evaluating a new method for touch DNA extraction on cartridge cases, comparing yield and quality effects for forensic firearm analysis. Experiment design, procedure, and findings discussed. Contact provided for inquiries.

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Impact of Submersion DNA Extraction on Firearms Examination

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  1. Impacts of Submersion DNA Extraction on Firearms Examination of Cartridge Cases Elizabeth Bustamante Firearms Examination Unit Washington DC Department of Forensic Sciences

  2. Retrospective Pilot Study • New method of extracting touch DNA • Montpetit & O’Donnell- 2015 • 34.7% yield DNA compared to 23.6% yield DNA with swabbing method • “Dunking” is already happening • San Diego • Signature Science validation study • Requests by USAO • No previous consultation of Firearms SMEs • Oxidation concerns noted

  3. DNA Extraction Method Alternative to swab/tape or gel lift Premise: touch DNA collection & extraction will yield more DNA without additional substrate Can be used with organic and non-organic lysis buffers Submersion with incubation

  4. Test Design • Purpose: determine what (if any) factors of dunking process affect Firearms examination • Does dunking have any effect on tool mark quality/ability to make an ID? • Procedural concerns: type of evidence submitted? Type of method used? Time/temperature concerns for reaction with metal? • Round 1 • Caliber, buffer type, submersion time, metal composition • Round 2 • Buffer type, metal composition, rinse, packaging, time

  5. Round 1 Tests: Variables • Caliber • 9mm Luger, .40 S&W, .45 auto • Buffer Type • Inorganic (chaotropic salts), organic (phenol/chloroform), deionized water (control) • Submersion Time • 30 mins, 120 mins • Case/Primer Metal Composition • Brass/Nickel (GFL/Fiocchi), Brass/Copper (Federal NonToxicBallisticlean), Aluminum/Nickel (CCI NR), Steel/Brass (Wolf Performance)

  6. Round 1 Tests: Procedure Sample preparation Test Fire Pre-test comparisons & NIBIN entry Lysis buffer preparation Submersion w/ incubation at 56oC Samples dried, rinsed & dried again Post-test comparisons & NIBIN entry

  7. Round 1 Tests: Evaluation • Microscopic examination • Conclusions: • Identification • Elimination • Inconclusive • Unsuitable • NIBIN • Effect seen in imaging technology- background noise

  8. Round 1 Tests: Results & Impact • Microscopic examination • No effect on ability to ID • Firing pin & breech face marks consistent within ammunition types • Post-dunking CCI cases- clear lacquer • NIBIN • Changes in background noise • No more than differences between ammunition brands .40 S&W Pre-test ID

  9. Round 2 Tests: Variables • Buffer Type • Inorganic (chaotropic salts), organic (phenol/chloroform), deionized water (control) • Case/Primer Metal Composition • Brass/Nickel (GFL/Fiocchi), Brass/Copper (Federal NonToxicBallisticlean), Aluminum/Nickel (CCI NR), Steel/Brass (Wolf Performance) • Rinse • Rinse w/ deionized water/no rinse • Packaging • Paper envelope/plastic bag • Time • Three evaluations: immediately after dunking, after 3 months, after 6 months

  10. Round 2 Tests: Procedure Sample preparation Test Fire Pre-test comparisons Lysis buffer preparation Submersion w/ incubation at 56oC for 120 mins Samples rinsed (if applicable) & dried Post-test comparisons (w/ storage at room temp for 3-month intervals)

  11. Round 2 Tests: Evaluation • No NIBIN • Samples evaluated in comparison to sample #1 (unaffected) • Identification determined • Changes noted: residue, color, oxidation/rust, quality of marks • Green: no discernable change over time • Yellow: changes noted are minor- do not affect examination • Orange: changes noted are moderate- could affect examination • Red: changes noted are severe- presents concern for examination

  12. Round 2 Tests: Results

  13. Round 2 Tests: Results

  14. Round 2 Tests: Impact

  15. Round 2 Tests: Impact

  16. Continuing Potential • Evaluation with virtual microscopy • Quantitative evaluation • Lab-specific procedure differences • Other extraction buffer reagents • Incubation temperature variable • Other cartridge case variables: • Older samples • Damaged samples • Firearm types/more challenging IDs

  17. Questions/Contact Elizabeth Bustamante Forensic Scientist II | Firearms Examination Unit (FEU) DC Department of Forensic Sciences (DFS) Office: 202-727-3280 | Email: elizabeth.bustamante@dc.gov 401 E. Street SW | Washington DC, 20024 | www.dfs.dc.gov

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