ForensicCONNECT 29 September 2014
Low copy number (LCN) typing is a general technique used for analyzing low-quantity DNA samples. Short tandem repeat (STR) testing on aged and extremely limited samples, such as “touch DNA” samples, has increased over the past decade. Samples with low quantities of template DNA are typically subjected to exaggerated stochastic effects during the polymerase chain reaction (PCR) that impact the reproducibility and reliability of DNA typing results.
Download PhD Thesis by Pamela L Marshall (226 pp)
Australian Journal of Forensic Sciences Vol. 46, Issue 4, 2014 James Robertson pp. 365-367
The Canberra Times reports that Dr Bob Moles, Coordinator, Networked Knowledge, has told them that ‘A Royal Commission should be held into the forensic procedures that have been operating in Australia for the past 20 years in light of the inquiry findings into the murder conviction of David Harold Eastman’.
Dr Moles likened errors in the Eastman case to the Splatt and Chamberlain cases from the 1980s and is quoted as saying ‘Forensic evidence experts told the royal commission that every piece of evidence was flawed.’ It is not entirely clear if Dr Moles was referring in this statement to the Splatt and/or the Chamberlain case. As I was one of the ‘forensic evidence experts’ who assisted the Royal Commission into the conviction of Splatt, his statement is unhelpful and a gross oversimplification.
Notwithstanding, and regrettably, the Report to the Board of Inquiry into the conviction of David Harold Eastman for the murder of Colin Stanley Winchester does not make pleasant reading from a forensic viewpoint.
Posted in Clinical forensic medicine, Drug analysis and toxicology, Forensic DNA, Forensic pathology, Leadership / Management, Physical evidence, zJournal articles
Tagged Australia, Forensic science;, Forensic testing, Gunshot residues, Police investigations
Journal of Forensic Sciences , Issue 5, pages 1343–1350, September 2014
Forensic practitioners and crime laboratories regularly collect and analyze fingernail evidence; however, the best techniques for processing such evidence have not been established. In this study, numerous aspects of fingernail evidence processing—collection of exogenous cells, transportation, purification of DNA, and STR analysis—were analyzed using fingernails harboring applied blood or epithelial cells from scratchings. Autosomal STR mixtures resulted when fingernails were soaked or swabbed, while scrapings rarely generated mixtures but exhibited allelic dropout. Y-STRs yielded single source profiles, with scrapings again showing dropout. A silica-based kit extraction recovered significantly more exogenous DNA than did organic extraction, neither of which was affected by nail polish. Swabbing nails in succession resulted in some cross-contamination from exogenous material, while transporting nails together did not, although there was loss of exogenous cells. Optimized nail processing produced complete Y-STR profiles of male volunteers from female fingernails following scratchings.
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Forensic Science, Medicine, and Pathology September 2014, Volume 10, Issue 3, pp 322-328
The breakdown of DNA and RNA in decomposing human tissue represents a major obstacle for postmortem forensic molecular analysis. This study investigated the feasibility of performing PCR-based molecular analysis of blood and muscle tissue from 45 autopsy cases with defined postmortem intervals ranging from one to more than 14 days. It was not possible to collect blood from 38 % of the autopsy cases due to severe coagulation and hemolysis, whereas muscle tissue was available for all cases. PCR-amplifiable DNA could be extracted from 96 % of the frozen muscle specimens and from 93 % of the formalin fixed and paraffin embedded (FFPE) muscle specimens. A quality assessment of muscle-derived DNA showed increased fragmentation with advancing body decomposition and generally more fragmentation in DNA from FFPE tissue than in DNA from frozen tissue. It was possible to amplify 1,000 basepair (bp) DNA fragments from all samples with postmortem intervals below 3 days whereas 400–600 bp long fragments typically could be amplified from the most decomposed muscle specimens. RNA was less stable than DNA in postmortem muscle tissue, yet selected mRNA molecules could be detected by reverse-transcriptase PCR in all samples up to 3 days after death. We conclude that analysis of DNA from bodies with a wide postmortem interval range is usually possible whereas the consistency of RNA analyses decreases considerably 3 days postmortem. We showed that muscle tissue is a highly usable source of DNA and RNA for postmortem forensic molecular analysis as well as for retrospective research projects based on archived FFPE specimens.
Forensic Science, Medicine, and Pathology September 2014, Volume 10, Issue 3, pp 336-343
To determine the detection frequency of spermatozoa in early evidence kit specimens and in subsequent full forensic specimens in alleged sexual assault.
Observational cohort study of 100 consecutive alleged sexual assault cases, presenting in Western Australia between 19th July 2008 and 6th February 2012, with both early evidence kit and full forensic evidence specimen collections. Eighty-eight cases were included in the study. Smears from all forensic specimens were analyzed by light microscopy to determine the detection frequency and structural characteristics of spermatozoa. Patient demographic features, characteristics of the alleged assault and details and timing of forensic collections were also recorded.
Spermatozoa were detected in early evidence kit specimens in 35 % (31/88) and in full forensic specimens in 42 % (37/88) of all cases (irrespective of type of alleged penetration). In alleged penile-vaginal penetration, spermatozoa were detected in early evidence kit specimens in 40 % (21/53) of cases when both first void urine and vulval gauze wipe were collected. Spermatozoa were detected in full forensic specimens in 45 % (31/69) of cases. Spermatozoa were detected in early evidence kit oral rinse specimens in 6 % (1/18) of cases of alleged penile-oral penetration and in early evidence perianal gauze wipe specimens in 33 % (2/6) cases of alleged penile-anal penetration. Spermatozoa were detected in the early evidence kit first void urine specimen in a single case, 11 % (1/9), in which the nature of the alleged assault was unknown. Spermatozoa were detected in early evidence kit specimens and not in full forensic specimens in 3 % (3/88) of cases.
Early evidence kit specimens are effective in recovery of spermatozoa, and in particular urine and vulval gauze wipe are worthwhile early forensic specimens for the detection of spermatozoa. Collection of early evidence specimens led to detection of spermatozoa-positive cases, which were not detected by subsequent full forensic specimen collection.
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Australian Journal of Forensic Sciences Volume 46, Issue 3, 2014
While there are many computer programs that derive the likelihood ratio for genetic and other types of evidence, the Bayesian method of combination of prior probability coupled with the likelihood ratio, used by courts to ascertain posterior probability, has less support from software and other practical aids. Without proper instructions to a court, Bayes’ rule is either applied subconsciously by the judge, or prior probability is, by default, assigned a flat 50% probability by a forensic expert. In the worst case, it can be interpreted wrongly. A graphical representation using a nomogram is a proven way of representing Bayes’ theorem but remains underused in the field of forensics and the law. For this paper, I used the freeware package PyNomo to prepare two simple forensic nomograms allowing the graphical calculation of posterior probability by increasing or decreasing the prior probability due to evidence.
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