Forensic application of a rapid one-step tetramethylbenzidine-based test for the presumptive trace detection of bloodstains at the crime scene and in the laboratory

How the forensic multidisciplinary approach can solve a fatal dog pack attack

The authors present the case of a 61-year-old man found dead in an agricultural plot. The first investigation of the scene revealed the corpse laid face up in a spot of partially dried blood, next to an olive tree. His face, arms, legs, and abdomen showed signs of severe contusion and laceration of dogs' bite wounds. Next to the victim, an olives bin had been found overturned on the ground. A multi-disciplinary approach, including crime scene analysis, autopsy findings, veterinary animals review, odontologist bite mark study, and forensic genetics DNA correlations, was performed. The present case is a documented watchdogs lethal pack attack and provides an example of how to recognize the more active participants thanks to their odontological alterations. It could be considered the first described dog pack attack case solved by dysgnathia alteration. Comparisons between the dental casts obtained from the dogs and the inflicted wounds were made, resulting in positive correlations between the injuries and the dental arches from two of the six involved dogs, thanks to dental abnormalities and DNA founding. The victim's clothes were also compared with the dogs' dental casts, confirming that they were the most active participants during the pack attack. Dogs' DNA was finally matched with saliva traces found on victim's clothes and skin bite marks.

A comprehensive study into false positive rates for 'other' biological samples using common presumptive testing methods

The identification of biological fluids or materials in forensic samples is a key requirement in forensic science that relies on chemical and biological based tests, most of which exhibit false positivity. When reporting results from such tests, Forensic Scientists use words such as probable, possible, and likely, without always being able to provide robust support for these conclusions. In collating information about false positive rates for a number of these tests, we found limited research into the cross reactions observed from 'other' biological samples in commonly encountered case sample stains. By 'other' we mean biological fluids or materials that are not the primary target of the presumptive test being used. Here we carry out a specificity study to fill gaps in the literature for a number of the presumptive chemical, biological and immunochromatographic tests used to presumptively screen for blood, semen and saliva. The tests selected for this study are the widely used tests: Luminol, TMB/Combur³ Test® E, Kastle-Meyer (KM), RSID™ - Blood, ABAcard® HemaTrace®, Acid Phosphatase (AP), ABAcard® p30, RSID™ - Semen, Phadebas® 'Tube' Test, Phadebas® 'Press' Test, and RSID™ - Saliva tests. Specificity for each of these was tested in known samples, from volunteers, of blood, semen, saliva, urine, sweat, vaginal material, faeces and breast milk, and then false positive rates were determined.

A method validation for the hemoglobin chemical reagent test strip with the addition of ethylenediaminetetraacetic acid to increase the selectivity of this presumptive test for residual blood

Tetramethylbenzidine based chemical reagent test strips are often used in forensic science as a presumptive test for blood. These tests are designed as urinalysis test strips and include brands such as Combur®, HENSOTest®, Hemastix®, MultiStix® and Chemstrip®. They are used because they are simple to apply, stable, temperature tolerant and cost effective. The addition of a chelating agent, ethylenediaminetetraacetic acid increases the selectivity of this presumptive test for blood. This is a method validation for the hemoglobin chemical reagent test strip with EDTA. A range of substances, metal compounds, chemical solutions, blood and mixtures were tested in this method validation. The chelation with EDTA successfully prevented non-blood (false) positive results from all the substances tested and consistently produced a positive result for blood on a variety of surfaces. This study has shown that this method is capable of discriminating a blood stain on copper metal surfaces and eliminate the positive results generated by clean-up solutions such as hydrogen peroxide, which usually produce a positive result for most other presumptive tests for blood. This modified method is a simple, effective and reliable test for blood stains. A variety of variations were evaluated in this study. The simplest method of application was spraying the surface of the stain with a 0.5 M EDTA solution and testing the surface of the stain, and only requires a spray bottle of 0.5 M EDTA and the chemical reagent test strip. This spray approach is rugged and can be applied to horizontal, vertical and underside surfaces and requires little additional training. Overall, this study provides the forensic science community with an improved method more easily used, stored, transported and selective for blood, than luminol and safer than TMB.

Blood and sperm traces on human hair. A study on preservation and detection after 3-month outdoor exposure

Hair can retain important biological traces for forensic investigations. Forensic scientists are used to looking for such traces on clothing and skin of victims, however, when decomposition kicks in and all that remains of the victims is the skeleton, hair may be the only tissue representing the surface of the body at the time of a crime on which biological traces of an aggressor may have been left and still be detectable. Given the lack of research on this topic, this pilot study aims to assess the capacity of hair to retain semen and blood in hair, and the possibility to detect these fluids with well-known techniques and to obtain a useful genetic profile even when exposed to environmental conditions (Open Natural Environment (woods), Open Man Made Environment (urban)) for three months. Results showed that both traces were always visible and detectable with almost all techniques in the Control Environment, while in the two open environments some difficulties arose. However, biomolecular analysis was effective up to three months on both fluids in the Natural Environment and up to two months and one week respectively on blood and semen in the Man Made Environment. The Combur Test, OBTI, and Luminol were effective on blood up to three months in both environments while Sperm-HY-Liter and observation of cellular components were effective on semen up to at least 1 month and PSA testing was positive up to 1 week in both environments. The present work can be considered an encouraging starting point for the analysis of biological traces on hair in forensic contexts, regardless of the PMI, since blood and semen related to a crime may survive.