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Ahlinder J.,Swedish Defence Research Agency | Nordgaard A.,Swedish National Forensic Center | Lindstrom S.W.,Swedish Defence Research Agency
Journal of Chemometrics | Year: 2015

Forensic statistics is a well-established scientific field whose purpose is to statistically analyze evidence in order to support legal decisions. It traditionally relies on methods that assume small numbers of independent variables and multiple samples. Unfortunately, such methods are less applicable when dealing with highly correlated multivariate data sets such as those generated by emerging high throughput analytical technologies. Chemometrics is a field that has a wealth of methods for the analysis of such complex data sets, so it would be desirable to combine the two fields in order to identify best practices for forensic statistics in the future. This paper provides a brief introduction to forensic statistics and describes how chemometrics could be integrated with its established methods to improve the evaluation of evidence in court. The paper describes how statistics and chemometrics can be integrated, by analyzing a previous know forensic data set composed of bacterial communities from fingerprints. The presented strategy can be applied in cases where chemical and biological threat agents have been illegally disposed. © 2015 John Wiley & Sons, Ltd. Source

Hedman J.,Swedish National Forensic Center | Hedman J.,Lund University | Agren J.,Swedish National Veterinary Institute | Ansell R.,Swedish National Forensic Center | Ansell R.,Linkoping University
Forensic Science International: Genetics Supplement Series | Year: 2015

A possible alternative to conventional stain recovery by swabbing, taping or cutting, is the M-Vac wet-vacuum instrument (M-Vac Systems Inc.). We have evaluated M-Vac for sampling of dried saliva on porous and non-porous surfaces, shed cells on clothes and touch DNA. M-Vac gave significantly higher DNA yields for dried saliva stains on laminated wood, compared with cotton swabs (average DNA concentrations 1.14 vs. 0.57. ng/μL, p = 0.02). For stains on glass, M-Vac and cotton swabs gave comparable DNA yields. Additionally, M-Vac retrieved three times as much DNA from saliva stains on cotton fabric (T-shirt) compared with saliva on towels (terry cloth), showing that the absorption properties of the surface affect wet-vacuum sampling. M-Vac was also applied for retrieving wearer DNA from clothes, enabling generation of complete DNA profiles from denim jeans, leggings and cotton T-shirt. A mixed DNA profile was retrieved from an "aggressor" pressing a hand against the shoulder area of a worn T-shirt. Since the major component of the obtained mixed DNA profile was from the wearer, M-Vac may not be ideal for touch DNA sampling of clothes. Wet-vacuum sampling requires a fairly large instrument, trained users and DNA extraction procedures handling large sample volumes. The complexity of M-Vac sampling prevents it from being extensively used, but in specific and important cases it can be a valuable sampling tool. © 2015 Elsevier Ireland Ltd. Source

Boiso L.,Swedish National Forensic Center | Sanga M.,Swedish National Forensic Center | Hedman J.,Swedish National Forensic Center | Hedman J.,Lund University
Forensic Science International: Genetics Supplement Series | Year: 2015

Forensic DNA analysis is partly limited by PCR-inhibitory compounds present in the DNA extracts. Generally, these inhibitors disturb amplification, i.e., the production of amplicons. We have found that dithiothreitol (DTT) from the DNA extraction process can cause another type of real-time PCR disturbance, i.e., inhibition of signal detection through fluorescence quenching. DNA extracts containing DTT substantially quenched the passive reference signal in the Quantifiler HP DNA Quantification kit. This quenching resulted in overestimation of DNA concentrations, as target DNA signals are normalized to the passive reference signal. © 2015 Elsevier Ireland Ltd. Source

Sanga M.,Swedish National Forensic Center | Boiso L.,Swedish National Forensic Center | Lindsten H.,Swedish National Forensic Center | Radstrom P.,Lund University | And 4 more authors.
Forensic Science International: Genetics Supplement Series | Year: 2015

PCR inhibition is a critical parameter in forensic DNA analysis. Substances interfering with amplification of short tandem repeats (STRs) may generate partial and/or ambiguous DNA profiles. We present a strategy for developing a broad panel of PCR-inhibitory reference materials (RMs), representing common casework samples. Our panel, including solutions prepared from for example cigarettes, chewing gum and soil, is a tool for in-house validation and lot testing of STR systems. PowerPlex ESX 16 Fast System tolerated high levels of some RMs, but several substances caused amplification problems. Humic acid had a negative effect on amelogenin, moist snuff hindered amplification of longer fragments, and chewing gum caused generally lowered allele peak heights. Applying a broad panel of RMs ensures that a wide range of inhibitory substances are tested, giving an improved understanding of inhibitor tolerance and effects. © 2015 Elsevier Ireland Ltd. Source

Forsberg C.,Swedish National Forensic Center | Wallmark N.,Swedish National Forensic Center | Hedell R.,Swedish National Forensic Center | Hedell R.,Chalmers University of Technology | And 5 more authors.
Forensic Science International: Genetics Supplement Series | Year: 2015

Tape-lifting is an efficient method for collecting traces of cellular material from fabrics. Since 2006, an in-house adhesive tape has been used in casework at the Swedish National Forensic Centre, Linköping. Although this tape gives good DNA yields, we aim to replace it with a commercial tape to save cost and labour. In order to enable a fair comparison between different adhesive tapes, we have developed and evaluated a method for production of relevant reference material. One person, known to be a good shedder, wore identical long-sleeved T-shirts under controlled circumstances, and trace recovery was systematically performed with the in-house tape (3 T-shirts, total of 24 samples). Each sample was DNA extracted and quantified to find the normal variation within the reference material. The DNA recovery differed considerably between samples, with DNA concentrations between 0.010-0.48. ng/μL (mean: 0.083, SD: 0.12. ng/μL). Applying such a reference material for comparison between two commercial tapes and our in-house tape resulted in mean DNA recoveries plus/minus one standard deviation of 0.013. ±. 0.006. ng/μL (Scenesafe FAST Box), 0.012. ±. 0.007. ng/μL (Touch tape), and 0.023. ±. 0.013. ng/μL (in-house tape). The in-house tape gave statistically significant higher yield compared to Touch tape (p <. 0.05), but for Scenesafe FAST Box the difference was not significant. The shedding of cells to clothes cannot be fully controlled. Having a systematically prepared, casework-like reference material with known variation is therefore vital for comparative studies of tapes. © 2015. Source

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