A 27‐Locus STR Assay to Meet All United States and European Law Enforcement Agency Standards,

Different national and international agencies have selected specific STR sets for forensic database use. To enhance database comparison across national and international borders, a 27‐locus multiplex system was developed comprising all 15 STR loci of the European standard set, the current 13 STR loci of the CODIS core, the proposed 22 STR loci of the expanded CODIS core, 4 additional commonly used STR loci, and the amelogenin locus. Development required iterative primer design to resolve primer‐related artifacts, amplicon sizing, and locus‐to‐locus balance issues. The 19.5‐min assay incorporated newly developed six‐dye chemistry analyzed using a novel microfluidic electrophoresis instrument capable of simultaneous detection and discrimination of 8 or more fluorescent dyes. The 27‐locus multiplex offers the potential for a new international STR standard permitting laboratories in any jurisdiction to use a single reaction to determine profiles for loci they typically generate plus an expanded common STR profiling set of global interest.     

Gorr on actus reus

Advances in forensic techniques have expanded the temporal horizon of criminal investigations, facilitating investigation of historic crimes that would previously have been considered unsolvable. Public enthusiasm for pursuing historic crimes is exemplified by recent high-profile trials of celebrities accused of historic sexual offences. These circumstances give new urgency to the question of how we should decide which historic offences to investigate. A satisfactory answer must take into account the ways in which the passage of time can erode the benefits of criminal investigation, the costs associated with investigating old crimes, and the need to prioritize investigations in the face of limited police resources. This article emphasizes the first of these factors. It begins by considering the moral goals of a criminal justice system and the contribution of criminal investigations to the achievement of these goals, distinguishing between contributions that depend on further steps in the criminal justice process, such as prosecution and punishment, and contributions that can have value independently of these further steps. Using this important distinction, the article then examines a range of factors that relate the passage of time to criminal justice goals, including the seriousness of the crime; deterioration of evidence; death of the offender, victim and others affected by the crime; and diminished psychological connectedness between those affected by the crime and their current selves. While the range and non-uniformity of relevant factors preclude a simple answer to the question of when historic crimes should be investigated and call instead for case-by-case assessment, we find that the analysis does support some general conclusions that can guide such an assessment.     

The role of criminal record in the federal sentencing guidelines

In this paper my concern is with the collective moral responsibility of criminal investigators for the outcomes of their investigations, bearing in mind that it is important to distinguish collective moral responsibility from, and relate it to, individual moral responsibility. In what sense, if any, are police detectives individually and collectively morally responsible for their success (or, for that matter, their failure) in gathering sufficient evidence to identify, arrest, and charge an offender who has committed a serious crime? Alternatively, in what sense are they morally responsible in cases where they identify, arrest, and charge an innocent person? And in what sense, if any, are police detectives individually and collectively morally responsible for the ultimate outcome of the trial, the finding by the courts of someone they have investigated and charged with a serious crime to be guilty or innocent?     

Simplified low-copy-number DNA analysis by post-PCR purification

Frequently, evidentiary items contain an insufficient quantity of DNA to obtain complete or even partial DNA profiles using standard forensic gentotyping techniques. Such low-copy-number (LCN) samples are usually subjected to increased amplification cylces to obtain genetic data. In this study, a 28-cycle polymerase chain reaction (PCR) was used to evaluate various methods of post-PCR purification for their effects on the sensitivity of fluorophore-based allelic detection subsequent to capillary electrophoretic separation. The amplified product was purified using filtration, silica gel membrane, and enzyme mediated hydrolysis purification techniques and evaluated for their effect on fluorescent allelic signal intensity. A purification method was selected and its effect on fluorescent allelic signal intensity was compared with that of the unpurified PCR product. A method of post-PCR purification is described which increases the sensitivity of standard 28-cycle PCR such that profiles from LCN DNA templates (<100 pg DNA) can be obtained. Full DNA profiles were consistently obtained with as little as 20 pg template DNA without increased cycle number. In mock case type samples with dermal ridge fingerprints, genetic profiles were obtained by amplification with 28 cycles followed by post-PCR purification whereas no profiles were obtained without purification of the PCR product. Allele dropout, increased stutter, and sporadic contamination typical of LCN analysis were observed; however, no contamination was observed in negative amplification controls. Post-PCR purification of the PCR product can increase the sensitivity of capillary electrophoresis to such an extent that DNA profiles can be obtained from <100 pg of DNA using 28-cycle amplification.     

A Study of PCR Inhibition Mechanisms Using Real Time PCR*,†

Abstract: In this project, real time polymerase chain reaction (PCR) was utilized to study the mechanism of PCR inhibition through examination of the effect of amplicon length, melting temperature, and sequence. Specifically designed primers with three different amplicon lengths and three different melting temperatures were used to target a single homozygous allele in the HUMTH01 locus. The effect on amplification efficiency for each primer pair was determined by adding different concentrations of various PCR inhibitors to the reaction mixture. The results show that a variety of inhibition mechanisms can occur during the PCR process depending on the type of co‐extracted inhibitor. These include Taq inhibition, DNA template binding, and effects on reaction efficiency. In addition, some inhibitors appear to affect the reaction in more than one manner. Overall we find that amplicon size and melting temperature are important in some inhibition mechanisms and not in others and the key issue in understanding PCR inhibition is determining the identity of the interfering substance.     

Determining the Source of Equine Bloodstains by Dinucleotide Repeats*

Abstract: A novel multiplex of independent dinucleotide tandem repeat (DTR) loci was previously described that is capable of not only discriminating human and equine DNA, but of identifying a single equine source. We report a case in which a bloodstained syringe and two needles were found during inspection of a barn by inspectors of the Pennsylvania Racing Commissions. Using the multiplex and single‐locus detection, all 21 equine DTR markers were detected in a suspect horse and two evidence samples, indicating the evidence samples came from the suspect animal. Only six markers were detected in the third evidence sample because the volume of blood was limited. Following whole‐genome amplification and single‐locus PCR, the third evidence sample detected a total of 17 markers and the likelihood of identity (probability from suspect horse/probability from a random pacer) was 7.0 × 10⁶. The DTR multiplex has some technical limitations, but it is already practical for casework.     

Investigation of Reproducibility and Error Associated with qPCR Methods using Quantifiler® Duo DNA Quantification Kit*

Abstract: Reproducibility of quantitative PCR results is dependent on the generation of consistent calibration curves via accurate volume transfers and instrument performance. A review of 14 standard curves, using two different QuantDuo^® standard DNA lots, showed variability of cycle threshold values between assays were larger than those of the Internal PCR Control (IPC). This prompted a set of experiments designed to determine the source of variability. Results showed that error introduced during DNA addition to the plate resulted in little variation. A comparison of seven independent series demonstrated cycle threshold variation between dilutions was larger than the variation expected from repeated samples. Modeling the influence of pipette errors on dilution series accuracy indicated that a more rigorous approach to external calibration curve production is required and showed that improvement in calibration curve stability is expected if the pipette conditions are carefully chosen and/or a single validated curve is utilized as the calibrator.     

Multicolor Real-Time PCR Genotyping of ABO System Using Displacing Probes

Abstract:  Rapid and informative ABO genotyping has become increasingly popular in forensic use. We developed a multiplex real-time polymerase chain reaction (PCR) approach to genotype ABO major groups and subgroups. Seven differently fluorophor-labeled displacing probes for O¹(261delG), A(261G), A(796C/803C), B(796A/803C), O² (802G>A), A² (1059delC), and A² (1009A>G) were combined in one or two PCRs to determine either ABO major groups or subgroups. The method correctly detected 13 reference DNA samples. A blind test of 237 samples resulted in complete agreement with their phenotypes, and 110 of these 237 samples as well as with PCR-SSP method. The whole analysis could be finished in less than 100 min at substantially low material cost and the template DNA ranging from 0.16 to 500 ng per reaction could be quantitatively detected. Despite the limited informativeness of ABO genotyping, the developed methods could find application in rapid and inexpensive screening of forensic settings.