Abstract:
Crime associated with firearms has become more common and widespread in New Zealand and in the rest of the world. The continuous growth of firearm related crime has increased the forensic interest in improving the evidence collection from firearms and ammunition. A large number of studies are being conducted in various jurisdictions in maximising DNA profiling results from firearms and ammunition. However, locating and collecting DNA from firearms and ammunition remains challenging and expensive.
The aim of this study was to bring together expertise from ESR with diamond dye, firearms and DNA extraction and from the New Zealand Police Fingerprints team to explore the potential of using diamond dye to locate touch DNA on cartridge cases. At the same time, this project investigated alternative DNA extraction methods in an attempt to improve the success rates of profiling touch DNA and to generate better investigative leads for the New Zealand Police.
The research was divided into four objectives where the first two objectives focused on the visualisation of touch DNA from cartridge cases and the second two objectives focused on improving DNA profiling results. The effect of fingermark enhancement on cartridge cases was investigated and it was found that the fingermark enhancement technique vacuum metal deposition (VMD) will significantly impact subsequent visualisations of DNA using diamond dye. It was also found that the application of diamond dye prior to VMD gave good results for both visualisation and enhancement of fingermarks. The impact of the process of firing on the presence of touch DNA on fired cases was investigated as the second objective and it was found that the process of firing has a significant impact on the presence of touch DNA.
The second two objectives of this research investigated methods in improving DNA profiling results from cartridge cases. The DNA IQTM extraction kit is used at ESR for the extraction of touch DNA samples. This research investigated two other extraction methods and compared these to DNA IQTM. The other two extraction methods used were QIAamp® DNA Mini kit coupled with a pre-extraction soaking method and QIAamp® DNA Mini kit coupled with direct lysis. The samples extracted using all these methods were amplified using Identifiler® Plus with standard PCR cycling conditions and Identifiler® Plus LCN with 34 cycles. In this objective it was found that the detection of allelic peaks was possible only with Identifiler® Plus LCN. Due to the very limited yield in DNA, the results obtained in this research cannot be interpreted quantitatively using statistics. However, a qualitative interpretation can be given, with the number of alleles obtained from all extractions across all the samples to conclude that direct lysis coupled with Identifiler® Plus LCN yielded the greater number of alleles.
The quantity of touch DNA on a sample is generally very minimal and if it is subjected to multiple steps of sampling and extraction, the chances of DNA getting lost during each step is high. This disadvantage in the multiple steps of processing samples for DNA profiling led to the investigation of the success rate of direct PCR from cartridge cases. Direct PCR was performed using Identifiler® Plus (28 cycles), Identifiler® Plus LCN (34 cycles) and Minifiler®. No results were obtained using Identifiler® Plus (28 cycles) and Minifiler®. Allelic profiles were obtained only from the direct PCR coupled with Identifiler® Plus LCN (34 cycles), however the admissibility and validity of the LCN amplification techniques depends on the replication of the results which is not possible in direct amplification. With the poor yield and profiling of touch DNA from cartridge cases, this study highlights the necessity of having extensive research regarding this matter.