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Our inquiry into forensic epistemology explores the use of data types for case-specific research within three pattern interpretation disciplines. It also examines the epistemic status of practition...

There is a recognized disconnect in priority and synergy between academic and practitioners in forensic science. In this work, we personally reflect on our experiences in conducting research studies that directly involve academic and practitioner stakeholders. We believe, amongst others, that this "gap" can be mitigated through regular and productive communication. We also emphasize the need to create stronger and national research strategies which identifies the current and pressing needs of enforcement officials in order to bring these needs directly to academia. As part of this, researchers should actively seek to make sure what they study will be relevant within the discipline. Our reflection is geared on direct feedback from an entomological study in large scale sampling of blowflies and workshops in bloodstain pattern analysis using a forensic blood substitute.

In recent years, crime scene analysis has been transitioning from being a technical discipline to being a scientific process. This progression is shifting the forensic practitioner examinin...

This work characterizes fundamental features of static drip patterns simulated for forensic bloodstain pattern analysis. The purpose of this study was to determine if and how two independent variables, impact velocity and droplet number, influence the parent stain size, shape and satellite spatter distribution of drip patterns created with whole ovine blood. To do this, 500 drip patterns were created in a controlled environment at five varying impact velocities and ten different droplet numbers on a hard paper surface. Digital images of the dried patterns were processed and analyzed using Fiji (ImageJ). The data collected from each pattern support the hypotheses that drip patterns contain predictable and reproducible elements based on impact velocity and droplet number. Basic fluid dynamic principles demonstrate that the size of the parent stains, as well as the number and distribution of satellite stains increase with increasing Weber number. A decrease in the circularity of the parent stains was also noted. This study provides fundamental qualitative and quantitative data on observable elements of drip patterns that can be used practically by bloodstain pattern analysts for pattern identification and classification.

This research validates the accuracy and efficacy of Sherlock, a recently developed program that estimates the area of origin (AO) of an impact pattern. Sherlock is an open-access, web-based softwa...

Peroxidase-based reagents that react with whole blood typically undergo internal quality control tests for reactivity prior to their use at a crime scene. This study presents a synthetic polymer alternative to using whole mammalian blood as a luminol reagent control testing material. The luminol-reactive polymer was developed by integrating horseradish peroxidase into a silicon-based sol-gel matrix. Liquid formulations of the polymer were made to simulate forensically relevant luminol reactivity with dried, whole ovine blood at dilutions up to 1:1 × 106. Photoemission from chemiluminescence reactions were characterized as a function of time using a SpectraMax® M3 microplate reader luminometer over a duration of three minutes. The maximum chemiluminescence intensity, time at maxima, reaction half-life, and overall behaviour of the sol-gels and two commercially available materials are reported. The behaviour of each material was statistically compared to the whole blood standards using a two-dimensional Kolmogorov-Smirnov test, which suggests that the sol-gels have a more realistic and statistically similar reactivity to neat (p = 0.835) and diluted (1:1 × 106) blood (p = 0.998) than the commercially available materials (p

This study explores the use of forensic synthetic blood substitute (FBS) for impact pattern simulation and area of origin estimation. Ten impact patterns were created at a known origin using the FB...

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.

This is the third in a series of articles reporting on forensic epistemology. Our first two research articles presented scientific results that are based in experimental design; including quantitative and qualitative responses from forensic science practitioners to scenarios and evidence. Based on a synthesis of this research there is evidence of a knowledge gap in formal reasoning for some forensic practitioners, and a limited understanding of case-specific research. Combining these results with a review of the current literature in the field of forensic reasoning, we now offer evidence of teaching and research strategies that can help increase the epistemic status (Confidence in, and justification of knowledge) of forensic science claims. This paper focuses on an integrated narrative review using hermeneutic methods of analysis to identify: (i) the epistemic state of forensic science; (ii) strategies to increase of knowledge; (iii) the need for collaboration between practitioners and academics; and, (iv) areas for future research.

This work explores the crown formation dynamics of blunt force impact onto a thin film of sheep's blood. Three weapons – a hammer head, a simulant baseball bat, and a metal bar – were used to impact blood on fibreboard, cloth, and sponge. Impact velocity was controlled using a custom impact device. High-speed videos were collected and analyzed with motion tracking and computing software. Interestingly, crowns were not observed to form in seven out of nine trials where each weapon struck the bloodied sponge. The widths and heights where observable crowns formed were measured and ranged between 0 to 105 mm and –0.4 to 36 mm, respectively. Bloodied material type was observed to influence the size and shape of the crown; however, the weapon heads used in this study did not. Three unusual cases of rim instability were observed where droplets were sent in the opposite direction of the expanding crown. This work supports the idea that the formation dynamics of mechanisms caused by blunt force impact are ...

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.

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.

This article explores the integration of innovative technologies into forensic science training initiatives and their effect on student engagement and depth of learning. Novel situation-oriented teaching practices were researched and implemented with the goal of enhancing the quality of practitioner forensic science training. Specifically, a basic bloodstain pattern analysis course was designed to provide and test technological-pedagogical innovations. University student surveys suggest that a combination of technologies that disentangle the complications of a crime scene is a reliable, engaging and effective approach for detailed training in bloodstain pattern analysis.

This research uses high-speed video analysis of bloodstain impact events to investigate the influence of impact velocity, fluid depth and free-space on the characteristics of the mechanism. We focus on the changes in the crown growth over time. This work demonstrates qualitative differences in the impact mechanism under a range of impact conditions. These differences are further explained quantitatively as a function of measured crown width and height lengths over time. Fluid dynamic explanations of this growth are featured in the results and discussion. A comparison to water dynamics is reported. Our image analysis demonstrates that droplets are consistently formed at points which are different from the impactor/fluid interface and that this difference is fluid dependent. This fluid dependency demonstrates the importance of accurately modeling fluid dynamics of blood when designing and deploying blood substitutes in forensics applications.

Blow fly (Diptera: Calliphoridae) larvae are commonly used in forensic cases to determine postmortem intervals using development rates and successional changes in community composition. Studies are conducted from different regions to provide these data. We wanted to know how widely applicable these data are. We examined whether urbanized landscapes have distinct urban blow fly communities or whether the community composition in urbanized areas is simply a variation of that found in the surrounding habitat or ecozone. Using liver baited traps, we sampled 7,272 flies from 32 sites across Canada and used mapping analysis to assess urban and rural landcover classifications, and compared urban and rural species abundance and composition. Blow fly species communities from urban areas across Canada were made up of similar species and differed from the communities found in nearby rural sites. Trapping at rural sites caught more blow flies compared with urban sites (mean flies/site 59.5 and 12.4). Of the 14 species caught, 8 were caught at urban sites, 61% of these being Cynomya cadaverina Robineau-Desvoidy, 14% Phormia regina Meigen, and 11% Lucilia sericata (Meigen). In rural sites, all 14 species were caught, 41% of specimens caught were P. regina, 21% C. cadaverina, 10% Calliphora vomitoria (Linnaeus), with only 4% L. sericata. These data suggest that regional studies are appropriate for forensic entomology applications in urban landscapes, given the similar trends across Canada, less so for wilderness or rural landscapes.

In this paper, we establish an impact pattern scene application method based on a zone stain selection model. This model had been developed within previous research and found to be relevant for improving accuracy for calculating an area of origin estimate. This theoretical model was tested as a method of training bloodstain analysts on how to select stains, and those data were compared with our scene application method. Several impact patterns were created within a laboratory environment and individual stains were selected according to rules of the theoretical model for both methods. The method includes the use of an overlay template that is placed on a computerized image of the end view of the pattern. A statistical analysis established that there was no significant difference between the theoretical model and the scene application method, indicating this method can be applied in crime scene analysis.

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.

This study investigates the chemiluminescent reaction of whole ovine blood with a luminol solution in a time and dilution series. Replicate samples of both fresh and dried certified pathogen-free ovine blood were prepared and diluted. Seven dilution conditions from neat to 1:1000000 were created for testing. A luminol solution, created using the standard Weber protocol, was applied to all samples in controlled laboratory conditions. A SpectraMax® M3 microplate reader luminometer was used to quantify the chemiluminescence from the reactions as relative luminescence units (RLUs) every four seconds for three minutes. Trends within and amongst the times series, reaction half-lives, and maximum chemiluminescent intensities are discussed. Our research provides a comprehensive dataset derived from instrumental and visual observations on the chemiluminescence resulting from ovine blood's reaction to luminol. This study has implications in forensic bloodstain pattern analysis as it offers a mixed method approach to characterizing the reaction between blood and a commonly used presumptive testing reagent.

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 fro...

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.

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 microL). 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 microL), drywall (0.37 m/sec, 1.7 microL), and wood (0.65 m/sec, 5.2 microL).

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 magnet's 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.

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.

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.