Trace DNA recovery rates from firearms and ammunition as revealed by casework data

DNA typing of cyanoacrylate fumed latent fingerprints using GlobalFiler™ and ForenSeq™ Signature Prep kits

DNA typing of latent fingerprints is highly desirable to increase chances of individualization. We recovered DNA from Cyanoacrylate (CA) fumed fingerprints and used both GlobalFiler™ and ForenSeq™ DNA Signature Prep kits for DNA typing. For GlobalFiler™, samples were processed using a protocol modified for Low Template (LT)-DNA samples (half-volume reactions, 30 cycles) while for ForenSeq™ DNA Signature Prep, samples were processed using a standard protocol and fluorometer-based library quantitation. We evaluated genotyping success and quality of profiles in terms of completeness, Peak Height Ratio/Allele Coverage Ratio, presence of PCR artifacts and drop-in alleles. With GlobalFiler™, average autosomal STR (aSTR) profile completeness was 44.4% with 2-20 pg, 54.3% with 22-60 pg, and 95% with 64-250 pg DNA input. CODIS uploadable profiles were obtained in 2/10, 3/11, and 11/12 samples in these ranges. With ForenSeq™ DNA Signature Prep, average aSTR profile completeness was 19.7% with 1-20 pg and 45.2% with 22-47 pg but increased to 78.3% with 68-122 pg and 86.7% with 618-1000 pg DNA input. Uploadable profiles were obtained in 0/12, 4/11, 4/7, and 3/3 samples for these ranges. Results show very high sensitivity using both kits. Half-volume reactions and 30 cycles had minimal negative effect on Globalfiler™ profile quality, providing support for wider use after validation experiments to routinely improve results from LT samples. A standard protocol for the ForenSeq™ DNA Signature Prep kit was also highly successful with LT DNA obtained from CA-fumed fingerprints with additional information from isometric STR alleles and other markers.

A systematic approach to the analysis of illicit drugs for DNA with an overview of the problems encountered

Due to the restricted nature of illicit drugs, it is difficult to conduct research surrounding the analysis of this drug material for any potential DNA in sufficient quantities acceptable for high numbers of replicates. Therefore, the current research available in peer reviewed journals thus far regarding analysing illicit drugs for DNA has been performed under varying experimental conditions, often using surrogate chemicals in place of illicit drugs. The data presented within this study originated from the analysis of genuine illicit drugs prepared both in controlled environments and those seized at the Australian border (and therefore from an uncontrolled environment) to determine if DNA can be obtained from this type of material. This study has been separated into three main parts (total n=114 samples): firstly, methamphetamine synthesised within a controlled environment was spiked with both saliva and trace DNA to determine the yield following DNA extraction; secondly, methamphetamine also synthesised in a controlled environment but on a larger scale was tested for the amount of DNA added incidentally throughout the synthesis, including the additional steps of recrystallising, homogenising and "cutting" the drug material to simulate preparation for distribution; and thirdly, the detection of human DNA within samples of cocaine and heroin seized at the Australian border. The DNA Fast Flow Microcon Device was utilised to concentrate all replicates from the same source into one combined extract to improve the DNA profiles for the samples where no DNA spiking occurred. Full STR profiles were successfully obtained from drug samples spiked with both saliva and trace DNA. Methamphetamine was present in the final DNA extracts and caused incompatibilities with the quantification of DNA using Qubit. The yields of DNA from drugs not spiked with DNA sources were much lower, resulting in 36 % of samples yielding alleles where all others did not. These results were not unexpected given these were realistic drug samples where the history of the drug material was unknown. This is the first study to obtain DNA profiles from genuine illicit drug material in both controlled and uncontrolled environments and indicates that the analysis of illicit drugs for DNA is an avenue worth pursuing to provide information which can in turn assist with disrupting the supply of these drugs. Given that DNA profiling is carried out worldwide using essentially the same systems as described within this study, the potential for impact is on a national and international scale.

Quantitative PCR overestimation of DNA in samples contaminated with tin

Metals can pose challenges while conducting forensic DNA analysis. The presence of metal ions in evidence-related DNA extracts can degrade DNA or inhibit PCR as applied to DNA quantification (real-time PCR or qPCR) and/or STR amplification, leading to low success in STR profiling. Different metal ions were spiked into 0.2 and 0.5 ng of human genomic DNA in an "inhibition study" and the impact was evaluated by qPCR using the Quantifiler™ Trio DNA Quantification Kit (Thermo Fisher Scientific) and an in-house SYBR Green assay. This study reports on a contradictory finding specific to tin (Sn) ions, which caused at least a 38,000-fold overestimation of DNA concentration when utilizing Quantifiler Trio. This was explained by the raw and multicomponent spectral plots, which indicated that Sn suppresses the Quantifiler Trio passive reference dye (Mustang Purple™, MP) at ion concentrations above 0.1 mM. This effect was not observed when DNA was quantified using SYBR Green with ROX™ as the passive reference, nor when DNA was extracted and purified prior to Quantifiler Trio. The results show that metal contaminants can interfere with qPCR-based DNA quantification in unexpected ways and may be assay dependent. The results also highlight the importance of qPCR as a quality check to determine steps for sample cleanup prior to STR amplification that may be similarly impacted by metal ions. Forensic workflows should recognize the risk of inaccurate DNA quantification of samples that are collected from substrates containing tin.

Impact of storage conditions and time on DNA yield from ammunition cartridges

Recovery of suitable amounts of DNA from ammunition cartridges for short tandem repeat (STR) or mitochondrial (mt) DNA analysis has been a challenge for crime laboratories. The metal composition of cartridge cases and projectiles exposes the DNA to harmful ions that damage and ultimately degrade the DNA such that it cannot be effectively amplified. The current study assessed the impact of time and storage conditions on touch DNA deposited on cartridge components of varying metal content: aluminum, nickel, brass, and copper. Elevated humidity levels facilitated greater DNA degradation and loss compared to low humidity (or "dry") conditions, indicating that recovered cartridge component evidence should be stored in a low-humidity environment immediately after collection, preferably with a desiccant. As expected, a relationship was observed between the amount of time elapsed since the cartridge components were handled and the associated DNA yield. Interestingly, while yields dropped considerably in the first 48-96 h post-handling, regardless of the storage conditions, a layering effect was observed that helps maintain a relatively constant level of surface DNA over extended periods of time. An apparent layering effect was also observed on cartridge components following multiple surface depositions, where yields were two times higher than single deposition samples at similar timepoints. Overall, these findings suggest that storage conditions and a layering affect play an important role in the preservation of DNA on ammunition components.

Touch DNA recovery from unfired and fired cartridges: Comparison of swabbing, tape lifting and soaking

Over the recent few years, several DNA collection techniques and methodologies have been published for the recovery of DNA from fired cartridge cases. In this study, swabbing, the DNA collection technique currently used in our jurisdiction (NSW, Australia), was compared with tape lifting and soaking to assess DNA recovery rates, DNA quality and profile quality. Brass .22LR and 9mmP cartridges were used as they are the most commonly encountered in our jurisdiction. The cartridges (n = 107) were loaded into cleaned firearm magazines by three volunteers of unknown shedder status, to mimic routine casework sample types. Half of the handled cartridges were fired whilst the other half were kept unfired. STR genotypes were produced at both 29 and 30 PCR cycles to evaluate which improved handler allele detection. DNA recovery rates showed that swabbing recovered significantly less DNA than tape lifting and soaking. Whilst there were no significant differences between tape lifting and soaking, tape lifting, on average, yielded more DNA than soaking. The calibre of ammunition had no influence on DNA recovery and in line with expectations, firing was found to decrease DNA recovery for all three sampling techniques. Assessment of DNA quality showed no evidence of PCR inhibition in any of the samples for this study. However, degradation indices showed that most samples were slightly to moderately degraded. Fewer handler alleles were detected from both fired tape lifted and soaked cartridges than unfired cartridges. Whilst 30 amplification cycles allowed for the detection of slightly more handler alleles, no statistically significant differences were found between 29 and 30 PCR cycles. Nonetheless, 50% of the profiles from unfired soaked cartridges that were non-uploadable after 29 cycles were uploadable after 30 cycles. Furthermore, 83% of profiles from unfired cartridges that were tape lifted were uploadable onto our jurisdiction's database at both 29 and 30 PCR cycles. All magazine controls, despite cleaning, contained some level of background DNA. Furthermore, increasing the number of PCR cycles to 30 also increased the detection of non-handler alleles in DNA profiles. Our results suggest tape lifting yields more uploadable profiles from unfired and fired cartridge cases than swabbing but also more adventitious (non-handler) alleles. However additional research will be needed to evaluate the full potential of this method.