Forensic Science Institute

Author: Dr. Mark McCoy – Page 7

Research: The Use of Image Analyzing Software for Muzzle to Target Distance Determination

Muzzle to target distance can be an important aspect in criminal investigations. For most distance determination opinions to be of value to an investigation, the range must be stated such that it gives meaningful information and the resulting bracket of muzzle to target distance must also be defended during courtroom testimony. Current measurement tools lead to subjective opinions by examiners. With objective measurements, examiners can provide improved investigative conclusions that may be defended in court with quantifiable data. Due to the rapid advancement in software technology in recent years, the ability exists to analyze targets with more accurate measurements. Currently, test targets are measured by approximate methods that utilize a high degree of subjectivity. This study examined the application of Image J, image-analyzing software, for use in determining muzzle to target distance. This research examined objective data to include particulate density and Gunshot residue dispersion and carried out a statistical replicate study to determine the number of targets needed at a given distance for each gun and ammunition combination. One pistol, revolver, rifle and shotgun were selected for this study. Test targets were shot five times at distances of: 4, 8, 12, 16, 20, 24 and 28 inches for the pistol, revolver and rifle, and at distances of: 4, 8, 12 and 16 feet for the shotgun. Visual and chemical examinations were performed on test targets using standard protocol procedures, published through the National Institute of Justice (NIJ) Distance Determination Training Module (2011). The targets were digitally photographed through each step and analyzed using the aforementioned protocol and Image J, image-analyzing software. Comparisons were made between the National Institute of Justice model and Image J. Data were obtained and reported using the image analyzing software for particulate count and GSR dispersion.

Posted on April 16, 2019 by Dr. Mark McCoy

Research: Identification of Mitochondrial Rodent DNA Isolated from Gnaw Marks on Skeletal Remains

A common problem encountered in forensic casework involving human skeletal remains is the inability to distinguish artifacts left on bones by scavengers from those associated with a victim’s death. If an artifact can be conclusively identified as scavenging marks, it will save valuable time and resources that might be spent processing it as possible evidence relating to the death of an individual. This research investigates the possibility of using DNA isolated from rodent buccal cells deposited on skeletal remains as a means of making such a distinction. Any DNA isolated from gnaw marks left on the remains will be amplified and sequenced using the cytochrome b gene in the mitochondrial genome as the target region. This genetic marker shows a high degree of differentiation between different species and allows for more definitive identification of the source of the artifact in question.

Posted on April 16, 2019 by Dr. Mark McCoy

Research: Comparative Analysis of Techniques for Shooting Trajectory Reconstruction

The field of shooting trajectory reconstruction is a common practice for law enforcement investigating crime scenes, though little history is actually known about the field. It is proposed that this study will advance crime scene knowledge of the field by applying common geometric principles and modern day crime scene reconstruction techniques. Through comparative analysis, this project will determine beneficial aspects of modern techniques. The study proposes a comparative analysis of two shooting scene reconstruction techniques; specifically, comparing the use of the Smart LevelÔ and calculations utilizing an angle finder to determine the efficiency of each technique. These aspects along with statistical data from crime scene investigators will contribute to the accuracy, precision, and error rate for both tools. This comparison and analysis will provide law enforcement with research enabling them to choose the most effective tool for crime scene analysis and aiding in validating the field of shooting trajectory reconstruction.

Posted on April 16, 2019 by Dr. Mark McCoy

Research: The Effects of Commercial Cleaning Agents on Automated DNA Extraction Efficiency and Genetic Profile Quality

As forensic DNA analysis has experienced countless advances in the past several decades, it has gained considerable notoriety among the general public, including those that are involved in the commission of crimes, leading to biological evidence that has been contaminated with various cleaning products in an attempt to conceal or destroy DNA evidence. This research examined the effects that three types of cleaning agents have on the ability of the Applied Biosystems^® Automate Express™ Forensic DNA Extraction System to efficiently extract high quality DNA free from inhibiting compounds using the Prepfiler Express™ Forensic DNA Extraction Kit. This study further assessed the impact that these chemicals have on the entire forensic DNA analysis process through evaluation of the quality of genetic profiles using a quantitative scale. A dilution series (neat to 1:1000) was prepared from whole human blood, as well as from a bleach product containing sodium hydroxide, a quaternary ammonium-based multi-surface cleaner, and a carpet cleaner with hydrogen peroxide as the active ingredient. Each blood dilution was combined with each dilution of the three cleaning products and each of those samples was analyzed in triplicate. The amount of DNA extracted from bleach-treated samples was reduced compared to corresponding control samples due to destruction of the DNA prior to extraction. The quantification results from samples treated with both the ammonium-based cleaner and the hydrogen peroxide carpet cleaner were similar to controls. The automated system successfully removed inhibitory compounds from samples containing sodium hydroxide and quaternary ammonium compounds, but the blood samples containing the concentrated hydrogen peroxide cleaner showed increased inhibition. The genetic profile quality scores indicated that the ammonium-based cleaner had no effect on profiles regardless of the dilution ratio of the sample, while samples containing at least equal amounts of bleach and blood can be expected to have complete dropout of all alleles. The inhibition previously mentioned due to the hydrogen peroxide carpet cleaner completely inhibited amplification in samples containing 1:100 or 1:1000 diluted blood treated with neat carpet cleaner. These results indicate that crime scene personnel should document any cleaning agents that may have contaminated biological evidence as it could significantly impact the results of DNA analysis depending on the type of product and its concentration in relation to the evidence.

Posted on April 16, 2019 by Dr. Mark McCoy

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