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When analysing blood spatters, traces often occur which regarding the collision angle, cannot be allocated to any supposed centre of origin. Drops following highly curved (ballistic) trajectories usually form these types of traces. The reconstruction of such trajectories requires knowledge of the mass, the diameter (of which approximations are known) and the velocity of the blood drops. This article provides an upper range of the velocity in relation to the diameter of the blood drops based on physical laws. This is very helpful in analysing ballistic trajectories.

•Conclusions by bloodstain pattern analysts were often erroneous and often contradicted other analysts.•On samples with known causes, 11.2% of responses were erroneous.•Both semantic differences and contradictory interpretations contributed to errors and disagreements. Although the analysis of bloodstain pattern evidence left at crime scenes relies on the expert opinions of bloodstain pattern analysts, the accuracy and reproducibility of these conclusions have never been rigorously evaluated at a large scale. We investigated conclusions made by 75 practicing bloodstain pattern analysts on 192 bloodstain patterns selected to be broadly representative of operational casework, resulting in 33,005 responses to prompts and 1760 short text responses. Our results show that conclusions were often erroneous and often contradicted other analysts. On samples with known causes, 11.2% of responses were erroneous. The results show limited reproducibility of conclusions: 7.8% of responses contradicted other analysts. The disagreements with respect to the meaning and usage of BPA terminology and classifications suggest a need for improved standards. Both semantic differences and contradictory interpretations contributed to errors and disagreements, which could have serious implications if they occurred in casework.

Expirated bloodstains are generated when blood is forcibly expelled from the mouth or upper airway due to air pressure. These patterns often contain biological constituents such as mucus and salivary enzymes, as well as distinctive morphological elements like bubble rings or beaded stains. However, their overall appearance can closely resemble that of impact or cast-off stains, which may lead to potential misinterpretation during forensic analysis. Conventional methods for reproducing expirated stains often rely on human subjects forcibly projecting blood or artificial substitutes, which pose limitations in terms of reproducibility, biosafety, and quantitative control. To address these challenges, this study presents the development of a bloodstain generation system capable of simulating expirated patterns under controlled airflow conditions. The system integrates anatomically informed 3D-printed oral models that simulate either blowing or coughing, combined with a calibrated airflow control unit and artificial blood formulated to match human rheological properties. This configuration enables precise modulation of airflow velocity and oral opening, allowing for consistent generation of expirated bloodstains. Morphological analysis was performed to quantify the area, impact angle, and orientation of stains produced under each condition. The results confirm the system’s ability to generate distinct patterns corresponding to different expiratory scenarios. This system provides a safe, reproducible, and quantifiable method for generating expirated bloodstains, offering significant utility in forensic training, as well as in generating machine learning and deep learning datasets for automated classification of bloodstain types. •Developed a controllable system for expirated bloodstain generation using anatomical oral models.•Simulated realistic blowing and coughing conditions by varying airflow velocity and oral aperture.•Generated reproducible mist-like or large droplet patterns depending on airflow configuration.•Analyzed stain morphology quantitatively using image-based measurements of area, angle, and orientation.•Provides a forensic tool for dataset creation and controlled experiments in bloodstain pattern analysis.

Bloodstain pattern analysis (BPA) on absorbent surfaces, such as fabrics, is far more complex compared to its application on smooth, hard, non-porous surfaces. Angle of impact and directionality are commonly interpreted from bloodstains but may be adversely affected by porous surfaces. In fact, there is a lack of evidence that traditional approaches to BPA are even applicable when blood impacts absorbent materials such as clothing and other fabrics. Hence, there is a critical need for research focusing on the validity and reliability of methods for bloodstain pattern analysis on textiles. Here, human blood drops were deposited on six different fabric types (cotton, satin polyester, rayon, blended polyester/spandex, blended nylon/spandex, and blended modal/polyester/spandex) at two known impact angles: 30° and 10°. Bloodstain morphology was found to be unique for each fabric. Calculated angles of impact for cotton and satin polyester were not statistically different from the known angle of impact while blended polyester/spandex, blended nylon/spandex, and blended modal/polyester/spandex significantly underestimated the known angle of impact. Even when stain morphology on fabric resembled those on a glass control, the angle of impact significantly underestimated the known. The ability to assign directionality based upon bloodstain morphology was dependent on the fabric type. These findings support the need for further research and the development of guidelines for bloodstain pattern interpretation on fabric materials. •Bloodstain area on some fabrics was smaller than glass despite evidence of wicking.•Impact angle varied with wicking and fabric thickness, roughness, and construction.•Known and estimated impact angles were consistent for cotton, polyester, and rayon.•On single knit fabrics, the known impact angle was underestimated.•The ability to assign directionality was dependent on the fabric type.

Bloodstain Pattern Analysis (BPA) helps us understand how bloodstains form, with a focus on their size, shape, and distributions. This aids in crime scene reconstruction and provides insight into victim positions and crime investigation. One challenge in BPA is distinguishing between different types of bloodstains, such as those from firearms, impacts, or other mechanisms. Our study focuses on differentiating impact spatter bloodstain patterns from gunshot backward spatter bloodstain patterns. We distinguish patterns by extracting well-designed individual stain features, applying effective data consolidation methods, and selecting boosting classifiers. As a result, our model exhibits competitive accuracy and efficiency on the tested dataset, suggesting its potential in similar scenarios. •A novel method distinguishes gunshot and impact bloodstain patterns using images.•Ellipse- and shade-based features improve interpretability and classification accuracy.•XGBoost achieves 92.89% accuracy, outperforming previous BPA models.•A new Stability Importance Score offers consistent feature ranking across model runs.•The method shows strong potential for practical forensic bloodstain analysis.

An improved automated bloodstain pattern analysis method has been developed and validated, which utilises computer vision techniques to identify bloodstains on a plain background within a digital image. The method generates metrics relating to the individual stains as well as the overall pattern, including bloodstain pattern specific metrics such as the gamma angle, circularity, solidity, area of convergence, stain density and pattern linearity. This method provides an objective approach to the analysis of bloodstains and bloodstain patterns and can generate a wealth of quantitative data that is currently not obtainable using manual techniques or other image-based programs currently utilised in the discipline. This method will be useful to analysts and researchers investigating the application of quantitative methods to bloodstain pattern analysis. •A method that automatically analyses digital images of bloodstain spatter patterns is described.•Improved stain segmentation detects even very small stains under varied lighting conditions.•A novel approach to fitting ellipses allows for accurate BPA specific metrics to be calculated.•Quantitative data is quickly and reliably extracted from patterns increasing objectivity.

This comparative review highlights the relationships between the disciplines of bloodstain pattern analysis (BPA) in forensics and that of fluid dynamics (FD) in the physical sciences. In both the BPA and FD communities, scientists study the motion and phase change of a liquid in contact with air, or with other liquids or solids. Five aspects of BPA related to FD are discussed: the physical forces driving the motion of blood as a fluid; the generation of the drops; their flight in the air; their impact on solid or liquid surfaces; and the production of stains. For each of these topics, the relevant literature from the BPA community and from the FD community is reviewed. Comments are provided on opportunities for joint BPA and FD research, and on the development of novel FD-based tools and methods for BPA. Also, the use of dimensionless numbers is proposed to inform BPA analyses.

The first point of contact between a spherical blood drop and a surface is related to the angle between the trajectory of the blood drop and the surface being struck. This angle is often referred to as the impact angle which can be estimated by knowing the width and length of the resultant elliptical bloodstain. Most software programs dedicated to area of origin analysis indicate the location of the backtracked bloodstain trajectory to be at the geometric centre or at the tip of the bloodstain ellipse. However, it is unknown how the first point of contact and the blood drop trajectory (here defined as the locus of the centre of mass of the drop as it travels) are related empirically. Thus, this study aims to look at how the initial point of contact and the trajectory at the impact of a blood drop relates to the formed bloodstain ellipse. Two volumes of blood (0.013 ml and 0.071 ml) were dropped from a height of 10 cm and 40 cm onto an inclined surface at 0°, 15°, 30°, 45°, 60°, and 75°. The transition from a spherical blood drop to an elliptically shaped bloodstain was recorded using a high-speed camera for all tests. A total of 72 ellipses were analyzed to determine the location of the first point of contact and trajectory point of the blood drop and how they relate to the formed elliptical bloodstain. A relationship was found between the first point of contact and the bloodstain trajectory which was dependent on the impact angle. However, there were clear deviations from theoretical assumptions due to blood drop oscillations, the effects of gravity, and the natural fluid characteristics of blood. The results of this study may assist bloodstain pattern analysts and software developers by more accurately applying the location of the blood drop trajectory based on empirical data. •The first point of contact follows a similar trend to the sine value.•The trajectory point moves along the half-length of the bloodstain.•The trajectory point and first point of contact are mainly at different locations.•The trajectory point is not always at the centre or tip of the ellipse.•The first point of contact is not always at the centre of tip of the ellipse.

We examined the drying characteristics of insect stains produced by the blow fly Calliphora vicina following ingestion of human blood using image analysis of stains deposited or produced on non-porous ceramic tile. The duration of drying and final morphologies of insect stains were influenced by ambient conditions (predominantly temperature), fluid volume, and time. The latter was most apparent with regurgitate stains, which typically required 2–3x longer to dry under ambient conditions than comparable sized bloodstains. As human blood dried on non-porous surfaces, a perimeter ring formed followed by radial cracks, and eventually lateral cracks between the radial lanes. The entire process occurred in > 10 min at 25 °C on ceramic tile when 2 µl of blood was deposited directly onto the tile surface. In contrast, regurgitate stains deposited directly by adult flies varied as to whether radial cracks formed. When radial cracks did form, they lacked symmetry like human bloodstains. Defecatory stains never formed contact lines at the perimeter, nor were radial or lateral cracks ever observed with dried fecal fluids. In experiments in which regurgitate was forcibly exuded from individual adult flies after consumption of human blood, the drying patterns were more consistent with blood than naturally deposited regurgitate in that many stains formed thickened perimeters and radial and lateral cracks during drying on ceramic tile. The results of this investigation indicate that some insect stains can be distinguished from human bloodstains based on morphological differences of dried stains when deposited on non-porous surfaces. •Drying characteristics of insect stains produced by Calliphora vicina were examined.•Regurgitate stains demonstrated shared some physical characteristics with human.•The radial racks of regurgitate stains were asymmetrical.•Regurgitate stains required a longer time to dry than human blood based on temperature and volume.•Drying of defecatory stains was unique from regurgitate and bloodstains.

•Bloodstain pattern analysis is a field of forensic science, and the need for experiments and education is emphasized for bloodstain analyst.•Through the development of appropriate blood substitute that can replace human blood, it can greatly help in the development of forensic science and bloodstain pattern analysis.•In the manufacture of blood substitute, the similarity between physical properties and drip bloodstain characteristics with human blood is very important.•It will be more efficient if various functions are complemented for practical use of blood substitute. Bloodstain pattern analysis, one of the areas of forensic science, is performed to analyze the physical characteristics of bloodstains, including their size, shape, and distribution, to reconstruct a crime scene. A bloodstain pattern analyst should obtain through experiments and education the capabilities to both understand the generation mechanisms of bloodstains and identify the characteristics of the bloodstains. Experiments and education about bloodstain pattern analysis are carried out by using human blood taken from subjects, animal blood (porcine or bovine) supplied from butcheries, and blood substitute products developed in other countries. However, these kinds of blood have many limitations in their application due to various problems. The blood substitute developed in the present study is more similar to human blood than other blood substitute products developed in other countries with regard to the physical properties, including viscosity, viscoelasticity, and surface tension, as well as the drip bloodstain patterns depending on the surface and coordinate characteristics of drip stains impact angle. The blood substitute developed in the present study is more practical, because the materials that are used in its preparation are readily available in the market and do not include chemicals that are harmful to the human body, and the blood substitute has luminol reaction functionality and pattern transfer bloodstain (bloodstain fingerprint, bloodstain footprint, etc.) dyeing functionality.