Single source DNA profile recovery from single cells isolated from skin and fabric from touch DNA mixtures in mock physical assaults

The ability to obtain DNA profiles from trace biological evidence is routinely demonstrated with so-called ‘touch DNA evidence’, which is generally perceived to be the result of DNA obtained from shed skin cells transferred from a donor's hands to an object or person during direct physical contact. Current methods for the recovery of trace DNA employ swabs or adhesive tape to sample an area of interest. While of practical utility, such ‘blind-swabbing’ approaches will necessarily co-sample cellular material from the different individuals whose cells are present on the item, even though the individuals' cells are principally located in topographically dispersed, but distinct, locations on the item. Thus the act of swabbing itself artifactually creates some of the DNA mixtures encountered in touch DNA samples. In some instances involving transient contact between an assailant and victim, the victim's DNA may be found in such significant excess as to preclude the detection and typing of the perpetrator's DNA. In order to circumvent the challenges with standard recovery and analysis methods for touch DNA evidence, we reported previously the development of a ‘smart analysis’ single cell recovery and DNA analysis method that results in enhanced genetic analysis of touch DNA evidence. Here we use the smart single cell analysis method to recover probative single source profiles from individual and agglomerated cells from various touched objects and clothing items belonging to known donors. We then use the same approach for the detection of single source male donor DNA in simulated physical contact/assault mixture samples (i.e. male ‘assailant’ grabbing the wrist, neck or clothing from the female ‘victim’, or being in transient contact with bedding from the ‘victim’). DNA profiles attributable to the male or female known donors were obtained from 31% and 35% of the single and agglomerated bio-particles (putative cells) tested. The known male donor ‘assailant’ DNA profile was identified in the cell sampling from every mixture type tested. The results of this work demonstrate the efficacy of an alternative strategy to recover single source perpetrator DNA profiles in physical contact/assault cases involving trace perpetrator/victim cellular admixtures.     

The use of the M-Vac® wet-vacuum system as a method for DNA recovery

Collecting sufficient template DNA from a crime scene sample is often challenging, especially with low quantity samples such as touch DNA (tDNA). Traditional DNA collection methods such as double swabbing have limitations, in particular when used on certain substrates which can be found at crime scenes, thus a better collection method is advantageous. Here, the effectiveness of the M-Vac® Wet-Vacuum System is evaluated as a method for DNA recovery on tiles and bricks. It was found that the M-Vac® recovered 75% more DNA than double swabbing on bricks. However, double swabbing collected significantly more DNA than the M-Vac® on tiles. Additionally, it was found that cell-free DNA is lost in the filtration step of M-Vac® collection. In terms of peak height and number of true alleles detected, no significant difference was found between the DNA profiles obtained through M-Vac® collection versus double swabbing of tDNA depositions from 12 volunteers on bricks. The results demonstrate that the M-Vac® has potential for DNA collection from porous surfaces such as bricks, but that alterations to the filter apparatus would be beneficial to increase the amount of genetic material collected for subsequent DNA profiling. These results are anticipated to be a starting point to validate the M-Vac® as a DNA collection device, providing an alternative method when DNA is present on a difficult substrate, or if traditional DNA collection methods have failed.     

Truancy Intervention Reduces Crime: Results from a Randomized Field Trial

Educational attainment is a fundamental cornerstone to success throughout the life-course. As a result, ensuring that young people remain in school and are not truant is critical. Although the importance of truancy as a risk factor for many adverse outcomes, including crime, has been well-documented, much less methodologically rigorous work has been undertaken to evaluate potentially promising prevention and intervention strategies. This paper uses a randomized field trial method to test how a partnership between police and schools targeting truancy impacts offending in a sample of high-risk truanting young people. We find that the truancy intervention reduces offending and we discuss the implications for practice and directions for future research.     

Artistic enhancement in the production of photo-fit likenesses: An examination of its effectiveness in leading to suspect identification

Following a crime, witnesses are often asked by the police to construct a Photo-FIT likeness of the suspect. However, previous laboratory research has indicated that the quality of the likenesses produced can be very poor. This study investigated whether the artistic enhancement of the basic Photo-FIT by a skilled operator using a variety of techniques influenced the quality of the Photo-FIT impression produced, and in turn increased the likelihood of correct recognition from the Photo-FIT. Six professional police Photo-FIT operators produced one basic Photo-FIT which was not artistically enhanced in any way and one Photo-FIT which had been artistically enhanced. These two types of Photo-FIT were given to 105 police recruits who were required to identify which face that Photo-FIT represented from a photographic lineup of 12 ‘suspect’ photographs. Composites which had been enhanced were significantly more successful in leading to a correct identification than were basic composites which had not been enhanced. The implications of these findings for police procedure and practice in the employment of commercial composite systems are discussed.     

The low income housing tax credit and racial segregation

This paper addresses a critical but almost unexamined aspect of the Low Income Housing Tax Credit (LIHTC) program – whether its use (and in particular, the siting of developments in high-poverty/high-minority neighborhoods), is associated with increased racial segregation in the metropolitan area. Using data from the Department of Housing and Urban Development (HUD) and the Census, supplemented with data on the racial composition of LIHTC tenants in three states, we examine three potential channels through which the LIHTC could affect segregation: where LIHTC units are built relative to where other low income households live, who lives in these tax credit developments, and changes in neighborhood racial composition in neighborhoods that receive tax credit projects. The evidence on each of these channels suggests that LIHTC projects do not contribute to increased segregation, even those in high poverty neighborhoods. We find that increases in the use of tax credits are associated with declines in racial segregation at the metropolitan level.     

Decomposition and Arthropod Succession in Whitehorse,Yukon Territory,Canada

Forensic arthropod succession patterns are known to vary between regions. However, the northern habitats of the globe have been largely left unstudied. Three pig carcasses were studied outdoors in Whitehorse, Yukon Territory. Adult and immature insects were collected for identification and comparison. The dominant Diptera and Coleoptera species at all carcasses were Protophormia terraneovae (R‐D) (Fam: Calliphoridae) and Thanatophilus lapponicus (Herbst) (Fam: Silphidae), respectively. Rate of decomposition, patterns of Diptera and Coleoptera succession, and species dominance were shown to differ from previous studies in temperate regions, particularly as P. terraenovae showed complete dominance among blowfly species. Rate of decomposition through the first four stages was generally slow, and the last stage of decomposition was not observed at any carcass due to time constraints. It is concluded that biogeoclimatic range has a significant effect on insect presence and rate of decomposition, making it an important factor to consider when calculating a postmortem interval.     

Analyzing Forensic Evidence Based on Density with Magnetic Levitation

This paper describes a method for determining the density of contact trace objects with magnetic levitation (MagLev). MagLev measurements accurately determine the density (±0.0002 g/cm³) of a diamagnetic object and are compatible with objects that are nonuniform in shape and size. The MagLev device (composed of two permanent magnets with like poles facing) and the method described provide a means of accurately determining the density of trace objects. This method is inexpensive, rapid, and verifiable and provides numerical values—independent of the specific apparatus or analyst—that correspond to the absolute density of the sample that may be entered into a searchable database. We discuss the feasibility of MagLev as a possible means of characterizing forensic‐related evidence and demonstrate the ability of MagLev to (i) determine the density of samples of glitter and gunpowder, (ii) separate glitter particles of different densities, and (iii) determine the density of a glitter sample that was removed from a complex sample matrix.