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Impacts of Submersion DNA Extraction on Firearms Examination of Cartridge Cases

Impacts of Submersion DNA Extraction on Firearms Examination of Cartridge Cases. Elizabeth Bustamante Firearms Examination Unit Washington DC Department of Forensic Sciences. Retrospective Pilot Study. New method of extracting touch DNA Montpetit & O’Donnell- 2015

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Impacts of Submersion DNA Extraction on Firearms Examination of Cartridge Cases

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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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