An ideal material for the preparation of known toolmark test impressions

Traditionally, toolmark test exemplars are produced by applying a tool's working surface to a piece of soft metal such as lead. Soft, pliable metals are primarily used for this purpose because they will replicate the microscopic grooves present on a tool's working surface without damaging the tool. In this paper the authors present an alternative material for the preparation of test toolmarks. Jewelry modeling or carving waxes are utilized in this study. These waxes are designed for the jewelry modeling industry to create very fine, highly detailed wax models of jewelry pieces that will be cast in various metals utilizing the lost wax casting method. Jeweler's waxes have been found to be ideal for preparing test toolmarks from exemplar tools. The test tool's working surface is applied to a piece of the appropriate wax in a manner consistent with the tool's design. The replicas obtained are exact, highly detailed, 1:1, negative impressions of the exemplar tools working surface, have a long shelf-life, and are suitable for use in toolmark examination and comparison cases.     

Blood droplet dynamics--I

The interpretation of bloodstain patterns at crime scenes has received increased attention in recent years. Important to an understanding of this is knowledge of the fundamentals of blood droplet formation and impact dynamics. A review of the literature reveals that a considerable amount of work has been done with aqueous drop dynamics. Workers in the forensic science area seem to have been unaware of this. In addition, some of the most important and comprehensive early work with blood droplet dynamics seems to have been forgotten. It is not cited in more recent publications dealing with bloodstain pattern interpretation. This literature is reviewed and discussed as well. The present study presents results of experiments with blood droplet dynamics and high-speed photographs of blood droplet impacts on stationary target surfaces. Some longstanding misconceptions of importance to forensic scientists engaged in crime scene reconstruction are discussed.     

Complex Congenital Heart Malformation Including Transposition of the Great Vessels,Presenting as Sudden Unexplained Infant Death

Transposition of the great vessels (TGV) is a common congenital heart defect that is difficult to diagnose before birth. Antenatal diagnosis is associated with increased survival. Unusual features such as anomalous pulmonary artery origin may delay cyanosis, decreasing clinical suspicion. A three‐week old female infant who had never been cyanotic presented for forensic autopsy due to onset of unresponsiveness at home. History included risk factors for TGV and signs of heart enlargement that were not recognized during life. Cardiac pathology consultation identified D‐type TGV with additional rare anomalies. TGV may present as sudden unexplained infant death (SUID) for forensic autopsy if variant features prevent development of cyanosis. Cardiac pathology consultation is helpful in clarifying these features.     

Blood droplet dynamics--II

An earlier companion paper to the present one dealt with a literature review as well as blood droplet formation and impacts to stationary target surfaces. The present paper discusses the results of experiments with moving target surfaces. These are discussed in the context of their correlation with blood droplet impacts to inclined stationary targets and with respect to the interpretation of bloodstain patterns at crime scenes where the target surface is capable of its own movement. A special belt device was designed and constructed for the experiments reported here. This motorized apparatus was used to drive paper belt target surfaces at various controlled speeds.     

Statistical discrimination of liquid gasoline samples from casework

The intention of this study was to differentiate liquid gasoline samples from casework by utilizing multivariate pattern recognition procedures on data from gas chromatography-mass spectrometry. A supervised learning approach was undertaken to achieve this goal employing the methods of principal component analysis (PCA), canonical variate analysis (CVA), orthogonal canonical variate analysis (OCVA), and linear discriminant analysis. The study revealed that the variability in the sample population was sufficient enough to distinguish all the samples from one another knowing their groups a priori. CVA was able to differentiate all samples in the population using only three dimensions, while OCVA required four dimensions. PCA required 10 dimensions of data in order to predict the correct groupings. These results were all cross-validated using the "jackknife" method to confirm the classification functions and compute estimates of error rates. The results of this initial study have helped to develop procedures for the application of multivariate analysis to fire debris casework.     

Preparation of Tool Mark Standards with Jewelry Modeling Waxes

Abstract:  This paper presents how jewelry modeling waxes are used in the preparation of tool mark standards from exemplar tools. We have previously found that jewelry modeling waxes are ideal for preparing test tool marks from exemplar tools. In this study, simple methods and techniques are offered for the replication of accurate, highly detailed tool mark standards with jewelry modeling waxes. The techniques described here demonstrate the conditioning and proper use of jewelry modeling wax in the production of tool mark standards. The application of each test tool's working surface to a piece of the appropriate wax in a manner consistent with the tool's design is clearly illustrated. The resulting tool mark standards are exact, highly detailed, 1:1, negative impressions of the exemplar tool's working surface. These wax models have a long shelf life and are suitable for use in microscopic examination comparison of questioned and known tool marks.     

Addressing the National Academy of Sciences' challenge: a method for statistical pattern comparison of striated tool marks

In February 2009, the National Academy of Sciences published a report entitled "Strengthening Forensic Science in the United States: A Path Forward." The report notes research studies must be performed to "…understand the reliability and repeatability…" of comparison methods commonly used in forensic science. Numerical classification methods have the ability to assign objective quantitative measures to these words. In this study, reproducible sets of ideal striation patterns were made with nine slotted screwdrivers, encoded into high-dimensional feature vectors, and subjected to multiple statistical pattern recognition methods. The specific methods employed were chosen because of their long peer-reviewed track records, widespread successful use for both industry and academic applications, rely on few assumptions on the data's underlying distribution, can be accompanied by standard confidence levels, and are falsifiable. For PLS-DA, correct classification rates of 97% or higher were achieved by retaining only eight dimensions (8D) of data. PCA-SVM required even fewer dimensions, 4D, for the same level of performance. Finally, for the first time in forensic science, it is shown how to use conformal prediction theory to compute identifications of striation patterns at a given level of confidence.     

Gunshot residue particle velocity and deceleration

The velocity of over 800 gunshot residue particles from eight different sources was determined using high speed stroboscopic photography (spark gap light source). These particles were found to have an average velocity of 500 to 600 ft per second. Many particles acquired considerably higher velocities. Thus, the particles have sufficient energy to embed themselves within certain nearby targets like skin or fabric. The relatively high velocity that the particles acquire explain the formation of stippling on skin in close proximity to a muzzle discharge. These findings also indicate little influence of air currents on particle behavior near the muzzle. The deceleration of less than 100 particles during a 100-microsecond interval was also calculated. The particles experienced rapid rates of deceleration which would explain why few particles are found in test firings beyond 3 ft from the muzzle of a discharged firearm. Because of their relatively high velocity, normal wind velocity would not be expected to significantly influence their motion near the muzzle.