Factors affecting DNA recovery from cartridge cases

Linda Jansson; Christina Forsberg; Yasmine Akel; Charlotte Dufva; Carina Ansell; Ricky Ansell; Johannes Hedman

doi:10.1016/j.fsigen.2020.102343

Factors affecting DNA recovery from cartridge cases

Forensic Sci Int Genet. 2020 Sep:48:102343. doi: 10.1016/j.fsigen.2020.102343. Epub 2020 Jul 3.

Authors

Linda Jansson¹, Christina Forsberg², Yasmine Akel¹, Charlotte Dufva², Carina Ansell², Ricky Ansell³, Johannes Hedman⁴

Affiliations

¹ National Forensic Centre, Swedish Police Authority, Linköping, Sweden; Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden.
² National Forensic Centre, Swedish Police Authority, Linköping, Sweden.
³ National Forensic Centre, Swedish Police Authority, Linköping, Sweden; Department of Physics, Chemistry and Biology, IFM, Linköping University, Linköping, Sweden.
⁴ National Forensic Centre, Swedish Police Authority, Linköping, Sweden; Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden. Electronic address: johannes.hedman@tmb.lth.se.

PMID: 32683317
DOI: 10.1016/j.fsigen.2020.102343

Abstract

Cartridge cases are often the sole items left behind after a shooting incident and DNA traces from these can identify persons connected to the shooting. However, the chance of retrieving usable DNA profiles from cartridge cases is limited, due to the low amounts of deposited DNA and subsequent DNA loss associated with the firing process. In the current study, we set out to increase the DNA recovery from cartridge cases and cartridges by evaluating different swab types and detergents used for trace collection. A protocol applying nylon-flocked swabs instead of cotton swabs was implemented in casework at the Swedish National Forensic Centre (NFC), increasing DNA yield. The number of samples providing a DNA concentration ≥ 0.001 ng/μL (the in-house cut-off for processing low-template samples) increased from 11.1 to 28.6 % for cartridge cases and from 16.0 to 43.3 % for cartridges. There was also a substantial increase in mixed STR profiles, too complex to use for comparisons. Thus, it was not possible to take the full advantage of the elevated DNA yield provided by nylon-flocked swabs. The number of usable STR profiles increased from 5.0 to 8.0 % for cartridge cases and remained unchanged for cartridges. Controlled studies were performed to assess the impact on the DNA recovery from different persons handling the ammunition, different material and size of the cartridge cases, and the type of firearm used. These studies reflected an ideal situation, where all cartridges were extensively handled and loaded without gloves, thus providing a higher expected DNA yield compared to most casework samples. The total peak height differed by up to a factor of ∼50 when 20 different persons handled cartridges prior to shooting. By evaluating eleven combinations of different firearms and ammunition, it was found that the casing material and type of firearm also have a substantial impact on DNA yield.

Keywords: Ammunition; Crime scene; Firearms; Nylon-flocked swab; Short tandem repeats; Trace DNA.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

DNA / analysis*
DNA Fingerprinting
Firearms*
Humans
Microsatellite Repeats
Specimen Handling* / instrumentation
Touch

Substances

DNA