Mike Illes

A Blind Trial Evaluation of a Crime Scene Methodology for Deducing Impact Velocity and Droplet Size from Circular Bloodstains

ABSTRACT: In a previous study, mechanical engineering models were utilized to deduce impact velocity and droplet volume of circular bloodstains by measuring stain diameter and counting spines radiating from their outer edge. A blind trial study was subsequently undertaken to evaluate the accuracy of this technique, using an applied, crime scene methodology. Calculations from bloodstains produced on paper, drywall, and wood were used to derive surface‐specific equations to predict 39 unknown mock crime scene bloodstains created over a range of impact velocities (2.2–5.7 m/sec) and droplet volumes (12–45 μL). Strong correlations were found between expected and observed results, with correlation coefficients ranging between 0.83 and 0.99. The 95% confidence limit associated with predictions of impact velocity and droplet volume was calculated for paper (0.28 m/sec, 1.7 μL), drywall (0.37 m/sec, 1.7 μL), and wood (0.65 m/sec, 5.2 μL).

Investigation of a Model for Stain Selection in Bloodstain Pattern Analysis

Abstract The selection of spatter stains from an impact pattern is the foundation by which the estimation of the area of origin is derived. In this paper we establish bloodstain selection criteria based on a statistical model. The model is constructed with data collected from several impact patterns created within a laboratory environment. The response variable considered is the distance between the known source and the estimated trajectory emanating from a stain; the explanatory variables are impact angle, glancing angle, zone location of the stain on the wall, and distance from the source to the wall. The model obtained indicates that zone location is relevant for improving accuracy, and that stains with any alpha angles can be used to calculate an area of origin estimation. Results from a validation study for the stain selection rules derived from the model are presented and analysed.

Affect of impact angle variations on area of origin determination in bloodstain pattern analysis

The estimation of the location of the area of origin of a blood source is of major importance within bloodstain pattern analysis. Given this, it is particularly important to establish the accuracy of such estimations. This study examines error rates by investigation of alpha angle inaccuracies of upward directional stains and compares a virtual bloodstain pattern model to real bloodstain patterns. It was found that the size of the area of origin influences the level of accuracy required in alpha angle estimations: larger areas of origin tolerated larger errors. Practical applications of the virtual model using real bloodstain patterns demonstrated that alpha angle measurements may show an inaccuracy of approximately 0-12° within a single pattern. The averaging process that occurs in estimating the area of origin lessens the influence of a few large variations, such that, there is no significant change in the area of origin estimation. The virtual model was validated as a conservative indicator, by means of overestimation, of the influence of alpha angle inaccuracy on area of origin. The study confirms that with proper stain selection, straight-line trajectories to estimate area of origin are valid and reliable.

Robust estimation for area of origin in bloodstain pattern analysis via directional analysis

Directional analysis provides quantitative data supporting the three-dimensional estimation of the area of origin for impact bloodstain pattern analysis. The final stage of directional analysis consists of calculating the point of origin via the arithmetic mean of top-view intersecting points and side-view heights of the virtual trajectories of single stains within the impact pattern. Given the sensitivity of the mean to the presence of outliers (droplets that have been influenced by gravitational force and aerodynamic drag), it is natural to ask whether directional analysis can be made more robust by modifying the averaging procedure. In this paper we focus our attention on two robust alternatives to the arithmetic mean: the trimmed mean and a deterministic version of the RANSAC algorithm. Our results suggest that the trimmed mean is a practical robust alternative to the arithmetic mean, whereas the deterministic RANSAC procedure is not. Since there can be no guarantee that stain selection can be free of outliers, the trimmed mean can be used as an aide in their detection. Moreover, our analysis reveals that the trimmed mean can also be used to detect outliers among the points of intersection of trajectories. Outliers of this type occur as the intersection points of trajectories emanating from stains with nearly vertical paths.

Confounding factors of fly artefacts in bloodstain pattern analysis

Abstract Few studies have explored the relationship between bloodstain patterns and fly artefacts. The documents reviewed in this paper focus on entomological activity at bloodletting scenes and methods describing how this can be interpreted. The methods used by various authors are discussed and categorized into visual, contextual and chemical analyses. Visual analyses focuses on the individual stains, contextual refers to the stains in the context of the scene and chemical analyses are those conducted on the stains to indicate source. Suggestions are made for future research needs in these categories, and current methods to employ are recommended.

The application of silicon sol–gel technology to forensic blood substitute development: Mimicking aspects of whole human blood rheology

Solution-gelation chemistry has promising applications in forensic synthetic blood substitute development. This research offers a silicon-based sol-gel approach to creating stable materials that share similar rheological properties to that of whole human blood samples. Room temperature, high water content, silicon sol-gels were created using the organosilane precursors 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate along with various concentrations of filler and pigment. Shear-thinning non-Newtonian properties were observed within most formulations of the presented materials. The effects of colloidal concentration, temperature, age and filler addition on the viscosity of the sol-gels were investigated. SEM-EDS analysis was used to identify the behavior of the fillers within the film and support their inclusion for basic bloodstain pattern simulation. A final proposed candidate sol-gel was assessed using a previously reported passive drip simulation test on a hard, dry surface and passed. This works represents encouraging development in providing safe material alternatives to using whole human blood for forensic training and research.

Design Considerations for the Implementation of Artificial Fluids as Blood Substitutes for Educational and Training Use in the Forensic Sciences

ABSTRACT Strengthening education and training in the forensic sciences requires the implementation of new and innovative technologies into existing teaching strategies. Scientific research in the design and use of artificial substitutes can offer new and advantageous contributions to such initiatives. This article describes the relevant considerations and advantages to designing a forensic blood substitute for use in forensic education and training facilities. BPA training materials must ensure safety, reliability, feasibility, and value added. Each of these considerations is addressed with a particular focus on the educational benefits (value added) that a forensic blood substitute can offer. In particular, the visual affordances of the material designed for this study will be highlighted in terms of its educational benefits to the training of scientists.

An Impact Velocity Device Design for Blood Spatter Pattern Generation with Considerations for High-Speed Video Analysis.

A mechanical device that uses gravitational and spring compression forces to create spatter patterns of known impact velocities is presented and discussed. The custom‐made device uses either two or four springs (k1 = 267.8 N/m, k2 = 535.5 N/m) in parallel to create seventeen reproducible impact velocities between 2.1 and 4.0 m/s. The impactor is held at several known spring extensions using an electromagnet. Trigger inputs to the high‐speed video camera allow the user to control the magnets release while capturing video footage simultaneously. A polycarbonate base is used to allow for simultaneous monitoring of the side and bottom views of the impact event. Twenty‐four patterns were created across the impact velocity range and analyzed using HemoSpat. Area of origin estimations fell within an acceptable range (ΔXav = −5.5 ± 1.9 cm, ΔYav = −2.6 ± 2.8 cm, ΔZav = +5.5 ± 3.8 cm), supporting distribution analysis for the use in research or bloodstain pattern training. This work provides a framework for those interested in developing a robust impact device.

Investigation of Physical Effects of Acid Yellow 7® Enhancement on Dark and Non-Porous Surfaces in Impact Pattern Area of Origin Estimation

Abstract Impact patterns that are generated on dark surfaces can become camouflaged creating difficulties with conventional photographic methods that are used when estimating the area of origin. Chemical enhancement is an alternative technique that can be used to visualize these latent bloodstains. The application of Acid Yellow 7 to already fixed bloodstains provides a robust enhancement protocol which yields minimal stain distortion. Image J software was utilized to count stains, resulting in an approximate 5% increase in small stain detection post-enhancement. Area analyses also performed with Image J demonstrates that the average area of a single stain increases by a factor of approximately 1.24 post-enhancement. When using the BackTrack™ suite of programs this enlargement does not significantly affect the calculated impact angle of an enhanced bloodstain when compared to that of its original deposition (P= 0.585). As a result, the area of origin can be estimated within the accepted error of ± 7 cm from the known blood source.

The application of silicon sol–gel technology to forensic blood substitute development: Investigation of the spreading dynamics onto a paper surface

This work investigates the spreading dynamics of three candidate sol-gel solutions, of ranging viscosities, surface tensions and densities, and compares them with water and two commercial blood substitute products. Droplets were created with different sizes (10 to75μL) and impact velocities (1.4 to 6.0m/s) to strike 176gsm cardstock. Over 2200 droplets were created using the six different fluids and their final dried stain diameter was measured. Droplet spread was plotted using the Scheller and Bousfield correlation and uses effective viscosity as a parameter for non-Newtonian fluids. Comparing the results to an expected whole human blood range validated the spread of the candidate FBS sol-gel material in passive drip bloodstain pattern simulation. These findings complement the practical application of the material as a safe substitute for demonstrating droplet spread under controlled conditions on hard paper surfaces.