The Dynamics of Blood Drop Release from Swinging Objects in the Creation of Cast-off Bloodstain Patterns.

Although the characteristics of cast-off bloodstain patterns are well known, the physics of the mechanism by which they are created is poorly understood. The aim of this work was to describe the process by which blood droplets disengage from swinging objects. Cast-off droplets were recorded using high-speed digital video photography, and the resulting cast-off patterns were analyzed to draw inferences about the trajectories of individual drops. Blood on the object's distal end formed ligaments, which subsequently disintegrated into droplets. Initial droplet trajectories were approximately tangential to the trajectory of the location on the object from which the droplet was released. The application of the laws of physics to the mechanism of cast-off is discussed, and the process of drop formation is compared to that of passive drop formation. A technical description of cast-off is proposed, and a diagram to aid investigators in interpreting cast-off patterns at crime scenes is offered.

Contextual information management: An example of independent-checking in the review of laboratory-based bloodstain pattern analysis.

This article describes a New Zealand forensic agency's contextual information management protocol for bloodstain pattern evidence examined in the laboratory. In an effort to create a protocol that would have minimal impact on current work-flow, while still effectively removing task-irrelevant contextual information, the protocol was designed following an in-depth consultation with management and forensic staff. The resulting design was for a protocol of independent-checking (i.e. blind peer-review) where the checker's interpretation of the evidence is conducted in the absence of case information and the original examiner's notes or interpretation(s). At the conclusion of a ten-case trial period, there was widespread agreement that the protocol had minimal impact on the number of people required, the cost, or the time to complete an item examination. The agency is now looking to adopt the protocol into standard operating procedures and in some cases the protocol has been extended to cover other laboratory-based examinations (e.g. fabric damage, shoeprint examination, and physical fits). The protocol developed during this trial provides a useful example for agencies seeking to adopt contextual information management into their workflow.

An image-processing methodology for extracting bloodstain pattern features.

There is a growing trend in forensic science to develop methods to make forensic pattern comparison tasks more objective. This has generally involved the application of suitable image-processing methods to provide numerical data for identification or comparison. This paper outlines a unique image-processing methodology that can be utilised by analysts to generate reliable pattern data that will assist them in forming objective conclusions about a pattern. A range of features were defined and extracted from a laboratory-generated impact spatter pattern. These features were based in part on bloodstain properties commonly used in the analysis of spatter bloodstain patterns. The values of these features were consistent with properties reported qualitatively for such patterns. The image-processing method developed shows considerable promise as a way to establish measurable discriminating pattern criteria that are lacking in current bloodstain pattern taxonomies.

The Reliability of Swipe/Wipe Classification and Directionality Determination Methods in Bloodstain Pattern Analysis.

Swipe and wipe are types of transfer patterns commonly encountered at bloodied scenes. So far, there have been little published data on the reliability of evaluating these patterns. In this study, 36 bloodstain patterns were randomly assigned to 12 analysts in three separate trials, and the analysts were required to evaluate the pattern type and directionality. The results revealed that correct classifications of patterns type were problematic, with an overall error rate of 32%. Wipes created from wet bloodstains were the most difficult to identify due to the absence of signs of alteration. The directionality of swipes made with a gloved finger had a 100% success rate; however, for swipes made with cloth, the analysts mistook the direction in nearly every case, which is of significant concern, considering these are common patterns at crime scenes. This study suggested there is a need for revising the current protocols for interpretation of these pattern types.

Passive Drip Stain Formation Dynamics of Blood onto Hard Surfaces and Comparison with Simple Fluids for Blood Substitute Development and Assessment.

The spreading dynamics of blood dripping onto hard surfaces is compared to two spreading models. Samples of human blood, porcine blood, and Millipore® water were dripped onto cardboard, foamcore, and glass surfaces in low velocity passive drip simulations. Final stain diameter, the total number of spines and scallops, and angle of impact were measured and analyzed. Spreading is best predicted by applying the concept of effective viscosity to the Scheller and Bousfield (R2  = 0.91) and Roisman (R2  = 0.89) spreading models. In the tested conditions, blood spreads with Newtonian tendencies; however, has quantifiable differences in stain appearance to Newtonian fluids like water. This is encouraging for the development of water-based fluids as synthetic blood substitutes (SBSs). The work presents an assessment platform to quantify and score the performance of simple water-based fluids using final stain diameter (6 points) and number of spines and scallops (6 points) at six dripping heights between 20 and 120 cm. The angle of impact of a stain alone is not a sensitive measure of SBS performance, but stain formation scores the SBS's performance with another 1 point. Together these features generate a quantitative relative ranking system, of a maximum possible 13 points, that can be used to support the use of a particular fluid for the creation of a drip stain. The performance of twenty simple fluids in the simulated dripping assessment test is described.

The Reliability of Pattern Classification in Bloodstain Pattern Analysis-PART 2: Bloodstain Patterns on Fabric Surfaces.

This study was designed to produce the first baseline measure of the reliability of bloodstain pattern classifications on fabric surfaces. Experienced bloodstain pattern analysts classified bloodstain patterns on pairs of trousers that represented three fabric substrates. Patterns also varied in type (impact, cast-off, expiration, satellite stains from dripped blood, and transfer) and extent. In addition, case summaries that accompanied each pattern contained contextual cues that either supported the correct answer (i.e., positive bias), were misleading toward an incorrect answer (i.e., negative bias), or contained no directional information (i.e., neutral). Overall, 23% percent of the resulting classifications were erroneous. The majority (51%) of errors resulted from analysts misclassifying satellite stains from dripped blood. Relative to the neutral information, the positive-bias information increased correct classifications and decreased erroneous classifications, and the negative-bias information decreased correct classifications and increased erroneous classifications. The implications of these findings for BPA are discussed.

Drip bloodstain appearance on inclined apparel fabrics: Effect of prior-laundering, fibre content and fabric structure.

The interaction of blood and fabrics is currently a 'hot topic', since the understanding and interpretation of these stains is still in its infancy. A recent simplified perpendicular impact experimental programme considering bloodstains generated on fabrics laid the foundations for understanding more complex scenarios. Blood rarely impacts apparel fabrics perpendicular; therefore a systematic study was conducted to characterise the appearance of drip stains on inclined fabrics. The final drip stain appearance for 45° and 15° impact angles on torso apparel fabrics (100% cotton plain woven, 100% polyester plain woven, a blend of polyester and cotton plain woven and 100% cotton single jersey knit) that had been laundered for six, 26 and 52 cycles prior to testing was investigated. The relationship between drop parameters (height and volume), angle and the stain characteristics (parent stain area, axis 1 and 2 and number of satellite stains) for each fabric was examined using analysis of variance. The appearance of the drip stains on these fabrics was distorted, in comparison to drip stains on hard-smooth surface. Examining the parent stain allowed for classification of stains occurring at an angle, however the same could not be said for the satellite stains produced. All of the dried stains visible on the surface of the fabric were larger than just after the impacting event, indicating within fabric spreading of blood due to capillary force (wicking). The cotton-containing fabrics spread the blood within the fabrics in all directions along the stain's circumference, while spreading within the polyester plain woven fabric occurred in only the weft (width of the fabric) and warp (length) directions. Laundering affected the formation of bloodstain on the blend plain woven fabric at both impact angles, although not all characteristics were significantly affected for the three impact conditions considered. The bloodstain characteristics varied due to the fibre content and fabric structure for both impact angles investigated. It is therefore necessary to consider the age of the fabric (which is fabric specific), the fibre type (including blends) and the fabric structure, before interpreting bloodstain patterns. An understanding of this simplified inclined drip stain interaction has been investigated to generate a basis for more complex interactions, such as spatter bloodstains.

The Reliability of Pattern Classification in Bloodstain Pattern Analysis, Part 1: Bloodstain Patterns on Rigid Non-absorbent Surfaces.

This study was designed to produce the first baseline measure of reliability in bloodstain pattern classification. A panel of experienced bloodstain pattern analysts examined over 400 spatter patterns on three rigid non-absorbent surfaces. The patterns varied in spatter type and extent. A case summary accompanied each pattern that either contained neutral information, information to suggest the correct pattern (i.e., was positively biasing), or information to suggest an incorrect pattern (i.e., was negatively biasing). Across the variables under examination, 13% of classifications were erroneous. Generally speaking, where the pattern was more difficult to recognize (e.g., limited staining extent or a patterned substrate), analysts became more conservative in their judgment, opting to be inconclusive. Incorrect classifications increased as a function of the negatively biasing contextual information. The implications of the findings for practice are discussed.

Impact dynamics of porcine drip bloodstains on fabrics.

As a passive blood drop impacts a hard surface, it is observed to collapse and spread laterally, then retract and settle. During the spreading phase, the edge of the drop may rise forming a crown extending into spines and breaking up into secondary drops. When a similar drop falls onto a textile surface these same processes may occur, but the process of blood wicking into the fabric complicates stain formation. These processes are described within for passive drip stains collected under controlled conditions using anticoagulated porcine blood. Three stages of this impact process were identified and could be separated into distinct time zones: (1) spreading (time t≤2.5ms) and (2) retraction (2.5≤t≤12ms) on the surface with potential splashing at the periphery, and (3) wicking (30ms ≤t≤30min) of the blood into the fabric. Although wetting and wicking may also occur for t<30ms, the vast majority of wetting and wicking occur after this time and thus the short-time wicking can be ignored. In addition, the number of satellite stains correlates with the surface roughness with the number of satellites for jersey knit>plain-woven>cardboard. Conversely, the size of the satellite stains correlates with the amount of wicking in the fabric with the satellite stain size for plain-woven>jersey knit>cardboard.

Bloodstain pattern classification: Accuracy, effect of contextual information and the role of analyst characteristics.

It is becoming increasingly apparent that contextual information can exert a considerable influence on decisions about forensic evidence. Here, we explored accuracy and contextual influence in bloodstain pattern classification, and how these variables might relate to analyst characteristics. Thirty-nine bloodstain pattern analysts with varying degrees of experience each completed measures of compliance, decision-making style, and need for closure. Analysts then examined a bloodstain pattern without any additional contextual information, and allocated votes to listed pattern types according to favoured and less favoured classifications. Next, if they believed it would assist with their classification, analysts could request items of contextual information - from commonly encountered sources of information in bloodstain pattern analysis - and update their vote allocation. We calculated a shift score for each item of contextual information based on vote reallocation. Almost all forms of contextual information influenced decision-making, with medical findings leading to the highest shift scores. Although there was a small positive association between shift scores and the degree to which analysts displayed an intuitive decision-making style, shift scores did not vary meaningfully as a function of experience or the other characteristics measured. Almost all of the erroneous classifications were made by novice analysts.

Exploring the role of contextual information in bloodstain pattern analysis: A qualitative approach.

During Bloodstain Pattern Analysis (BPA), an analyst may encounter various sources of contextual information. Although contextual bias has emerged as a valid concern for the discipline, little is understood about how contextual information informs BPA. To address this issue, we asked 15 experienced bloodstain pattern analysts from New Zealand and Australia to think aloud as they classified bloodstain patterns from two homicide cases. Analysts could request items of contextual information, and were required to state how each item would inform their analysis. Pathology reports and additional photographs of the scene were the most commonly requested items of information. We coded analysts' reasons for requesting contextual information--and the way in which they integrated this information--according to thematic analysis. We identified considerable variation in both of these variables, raising important questions about the role and necessity of contextual information in decisions about bloodstain pattern evidence.

A novel, element-based approach for the objective classification of bloodstain patterns.

The classification of bloodstain patterns has been identified as a challenging part of bloodstain pattern analysis due to the lack of a widely accepted and well-defined methodology and the ambiguity often associated with examining bloodstain patterns. The main aim of this study was to develop an objective, science-based method, for classifying bloodstain patterns, through the development of common language that could be used by BPA experts to describe the appearance of the pattern. This novel approach encourages a shift in the mindset of a BPA analyst by bringing them 'back to the basics' by treating components of a bloodstain pattern as discrete, observable and measurable units. One of the principal problems with current pattern classification methods is that pattern types are generally described in terms of the mechanism of pattern formation rather than grouping according to observable pattern characteristics. This study extends current BPA classification methodologies by developing and validating mechanism-free nomenclature that arises from observing and documenting the physical characteristics of bloodstain patterns. Following the grouping of bloodstain components on the basis of their physical characteristics, the formation evolution of these components is then investigated using concepts drawn from the fluid-dynamics of bloodstain pattern formation. This study offers a promising approach to distinguishing between different bloodstain pattern types through the use of visual aids in the form of colour maps, high-speed video and static digital images.

Systematic investigation of drip stains on apparel fabrics: The effects of prior-laundering, fibre content and fabric structure on final stain appearance.

Bloodstain pattern analysis is the investigation of blood deposited at crime scenes and the interpretation of that pattern. The surface that the blood gets deposited onto could distort the appearance of the bloodstain. The interaction of blood and apparel fabrics is in its infancy, but the interaction of liquids and apparel fabrics has been well documented and investigated in the field of textile science (e.g. the processes of wetting and wicking of fluids on fibres, yarns and fabrics). A systematic study on the final appearance of drip stains on torso apparel fabrics (100% cotton plain woven, 100% polyester plain woven, blend of polyester and cotton plain woven and 100% cotton single jersey knit) that had been laundered for six, 26 and 52 cycles prior to testing was investigated in the paper. The relationship between drop velocity (1.66±0.50m/s, 4.07±0.03m/s, 5.34±0.18m/s) and the stain characteristics (parent stain area, axes 1 and 2 and number of satellite stains) for each fabric was examined using analysis of variance. The experimental design and effect of storing blood were investigated on a reference sample, which indicated that the day (up to five days) at which the drops were generated did not affect the bloodstain. The effect of prior-laundering (six, 26 and 52 laundering cycles), fibre content (cotton vs. polyester vs. blend) and fabric structure (plain woven vs. single jersey knit) on the final appearance of the bloodstain were investigated. Distortion in the bloodstains produced on non-laundered fabrics indicated the importance of laundering fabrics to remove finishing treatments before conducting bloodstain experiments. For laundered fabrics, both the cotton fabrics and the blend had a circular to oval stain appearance, while the polyester fabric had a circular appearance with evidence of spread along the warp and weft yarns, which resulted in square-like stains at the lowest drop velocity. A significant (p<0.001) increase in the stain size on laundered blend fabric was identified. Bloodstain characteristics varied due to fibre content (p<0.001) and fabric structure (p<0.001). Blood on polyester fabric, after impact, primarily moved due to capillary force and wicking of the blood along the fibres/yarns, while for the cotton fabrics wicking was accompanied by movement of blood into the fibres/yarns. This study highlights the importance for forensic analysts of apparel evidence to consider the age, the fibre type and the fabric structure before interpreting bloodstain patterns.

Physical components of soft-tissue ballistic wounding and their involvement in the generation of blood backspatter.

Gunshot backspatter comprises biological material expelled backward through bullet entry holes. Crime scene investigators analyze backspatter patterns to infer wounding circumstances. An understanding of the mechanism of backspatter generation, and the relationship between spatter patterns and bullet and tissue characteristics, would enhance the predictive value of such analysis. We examined soft-tissue ballistic wounding responses to determine the underlying components and how these might be relevant to the generation of backspatter. We identified five mechanistic components to ballistic wounding (elastic, viscous, crushing, cutting, and thermal), each related to mechanical disciplines (respectively, solid mechanics, fluid mechanics, fracture mechanics, rheology, and thermodynamics). We identified potential roles for these five components in backspatter formation and provide a scenario whereby a sequence of events incorporating these components could lead to backspatter generation and expulsion. This research provides a framework for the mathematical representation, and subsequent computational predictive modeling, of backspatter generation and pattern formation.

Characterising the dynamics of expirated bloodstain pattern formation using high-speed digital video imaging.

During forensic investigations, it is often important to be able to distinguish between impact spatter patterns (blood from gunshots, explosives, blunt force trauma and/or machinery accidents) and bloodstain patterns generated by expiration (blood from the mouth, nose or lungs). These patterns can be difficult to distinguish on the basis of the size of the bloodstains. In this study, high-speed digital video imaging has been used to investigate the formation of expirated bloodstain patterns generated by breathing, spitting and coughing mechanisms. Bloodstain patterns from all three expiration mechanisms were dominated by the presence of stains less than 0.5 mm in diameter. Video analysis showed that in the process of coughing blood, high-velocity, very small blood droplets were ejected first. These were followed by lower velocity, larger droplets, strands and plumes of liquid held together in part by saliva. The video images showed the formation of bubble rings and beaded stains, traditional markers for classifying expirated patterns. However, the expulsion mechanism, the distance travelled by the blood droplets, and the type of surface the blood was deposited on were all factors determining whether beaded stains were generated.

The effect of firearm muzzle gases on the backspatter of blood.

Injuries caused by gunshots can produce what bloodstain pattern analysts know as "backspatter." Observations about the presence or absence of backspatter on an individual may be used in court as evidence of guilt or innocence. The discharge of three firearms (.22 caliber revolver, .38 caliber revolver, and .308 caliber rifle) and the resulting impact of bullets on a blood source were recorded using high-speed digital video imaging. Blood droplets, firearm muzzle gases, and ballistic shock waves were visualized using standard reflected light and shadowgraphy imaging techniques. A significant interaction between air currents, muzzle gases, and particulate material emanating from the firearms upon discharge with backspattered blood was observed. Blood droplets, initially spattered back toward the firearm and the shooter, were observed to change direction under the influence of firearm-induced air currents and were blown forward toward and beyond their original source location. Implications for experts testifying in court and for bloodstain pattern instructors are discussed.

Using oral microbial DNA analysis to identify expirated bloodspatter.

Distinguishing expirated bloodstains (blood forced by airflow out of the nose, mouth or a chest wound) from impact spatter (blood from gunshots, explosives, blunt force trauma and/or machinery accidents) is an important challenge in forensic science. Streptococcal bacteria are only found in the human mouth and saliva. This study developed a polymerase chain reaction (PCR) method that detects DNA from these bacteria as a sensitive tool to detect the presence of saliva. The PCR method was very specific to human oral streptococci, with no PCR product being made from human DNA or DNA from other microbes that were tested. It was also very sensitive, detecting as little as 60 fg of target DNA. The PCR amplification gave product with 99 out of 100 saliva samples tested. PCR was not inhibited by the presence of blood and could detect target DNA in expirated bloodstains in a range of materials and for up to 92 days after deposit on cardboard or cotton fabric. In a blind trial, the PCR method was able to distinguish three mock forensic samples that contained expirated blood from four that did not. Our data show that bacteria present in the oral cavity can be detected in bloodstains that contain saliva and therefore can potentially be used as a marker in forensic work to distinguish mouth-expirated bloodstains from other types of bloodstains.

Neural variability, detection thresholds, and information transmission in the vestibular system.

A fundamental issue in neural coding is the role of spike timing variation in information transmission of sensory stimuli. Vestibular afferents are particularly well suited to study this issue because they are classified as either regular or irregular based on resting discharge variability as well as morphology. Here, we compared the responses of each afferent class to sinusoidal and random head rotations using both information theoretic and gain measures. Information theoretic measures demonstrated that regular afferents transmitted, on average, two times more information than irregular afferents, despite having significantly lower gains. Moreover, consistent with information theoretic measures, regular afferents had angular velocity detection thresholds that were 50% lower than those of irregular afferents (approximately 4 vs 8 degrees/s). Finally, to quantify the information carried by spike times, we added spike-timing jitter to the spike trains of both regular and irregular afferents. Our results showed that this significantly reduced information transmitted by regular afferents whereas it had little effect on irregular afferents. Thus, information is carried in the spike times of regular but not irregular afferents. Using a simple leaky integrate and fire model with a dynamic threshold, we show that differential levels of intrinsic noise can explain differences in the resting discharge, the responses to sensory stimuli, as well as the information carried by action potential timings of each afferent class. Our experimental and modeling results provide new insights as to how neural variability influences the strategy used by two different classes of sensory neurons to encode behaviorally relevant stimuli.