The effect of fabric mass per unit area and blood impact velocity on bloodstain morphology

Influence of the relative humidity on the blood drip stain formation on jeans fabrics

The impact of whole human blood drops on jeans fabrics is studied as a function of the impact velocity U0, room relative humidity RH, and spacing S between the fabric and backing substrate. Experiments are performed with blood drops of the same initial diameter of D0 = 3 ± 0.08 mm and temperature of 37∘C. Whole human blood is collected from the same donor. The impact dynamics of blood drops is described as a function of U0 and S, and it is shown that the spacing has an effect on the splashing limit and the surface area of the drip stains. At RH = 30%, the drip stains (parent stains) after impact do not wick the fabrics. Moreover, the area of the drip stains increases with the impact velocity until a critical value (U0 = 3.3 ± 0.1 m∕s), where it becomes constant. A modified correlation is proposed to predict the drip stains area. At RH = 70%, the drip stains after impact wick the jeans fabrics. The area of the drip stains after impact is dependent on the impact velocity while the final area after wicking is not. Further, the contribution of the wicking, to the formation of the drip stains, decreases with the impact velocity. These findings show the importance of taking into account RH in future research work and in the analysis of the drip stains at crime scenes.

Forensic applications of micro-computed tomography: a systematic review

Purpose

The aim of this systematic review was to provide a comprehensive overview of micro-CT current applications in forensic pathology, anthropology, odontology, and neonatology.

Methods

A bibliographic research on the electronic databases Pubmed and Scopus was conducted in the time frame 01/01/2001–31/12/2021 without any language restrictions and applying the following free-text search strategy: “(micro-computed tomography OR micro-CT) AND (forensic OR legal)”. The following inclusion criteria were used: (A) English language; (B) Application of micro-CT to biological and/or non-biological materials to address at least one forensic issue (e.g., age estimation, identification of post-mortem interval). The papers selected by three independent investigators have been then classified according to the investigated materials.

Results

The bibliographic search provided 651 records, duplicates excluded. After screening for title and/or abstracts, according to criteria A and B, 157 full-text papers were evaluated for eligibility. Ninety-three papers, mostly (64) published between 2017 and 2021, were included; considering that two papers investigated several materials, an overall amount of 99 classifiable items was counted when referring to the materials investigated. It emerged that bones and cartilages (54.55%), followed by teeth (13.13%), were the most frequently analyzed materials. Moreover, micro-CT allowed the collection of structural, qualitative and/or quantitative information also for soft tissues, fetuses, insects, and foreign materials.

Conclusion

Forensic applications of micro-CT progressively increased in the last 5 years with very promising results. According to this evidence, we might expect in the near future a shift of its use from research purposes to clinical forensic cases.

Quantitative characterisation of ballistic cartridge cases from micro-CT

Evaluation of cartridge cases is essential within forensic ballistic analysis and is used in an attempt to establish a connection to the weapon used to fire it. This study consists of two experiments. The aims of Experiment 1 were to establish whether micro-CT is appropriate and repeatable for ballistic cartridge case analysis and if measurements can be extracted repeatably and reliably. Experiment 2 aimed to compare cartridge cases from two weapons to establish the magnitude of variation within and between weapons. A total of 48 cartridge cases fired by two distinct weapons were collected and micro-CT scanned to a high resolution. One randomly selected cartridge was scanned ten times under the same conditions to ensure repeatability of the scanning conditions in Experiment 1. Three novel measurements to quantitatively assess the firing pin impressions were proposed in Experiment 1 and comparatively analysed from two weapons in Experiment 2. Experiment 1 showed that micro-CT is an effective and highly repeatable and reliable method for 3-dimensional imaging and measurement of ballistic cartridge cases. Furthermore, high agreement for inter-rater reliability was found between five raters. Quantitative micro-CT analysis of the firing pin impression measurements in Experiment 2 showed a significant difference between the two studied weapons using Welch's t-test (p < 0.01). This study shows the advantage and reliability of utilising micro-CT for firing pin impression analysis. Quantitation of the firing pin impression allows distinction between the weapons studied. With expansion to further weapons, application of this methodology could complement current analysis techniques through classification models.

Effects of yarn size and blood drop size on wicking and bloodstains in textiles

Bloodstain pattern analysis (BPA) for stains found on non-porous surfaces has matured into a powerful forensic science tool based on fluid mechanics principles. The same cannot be said when bloodstains are found on porous substrates, such as textiles. This is partially due to the complex nature of textiles with tens of thousands of different materials in addition to unknown wear characteristics. In this study, three single jersey knit fabrics were manufactured from 100% cotton ring-spun yarns of linear densities of 12, 20, and 30 Ne (492, 295, and 197 dtex, respectively) and nearly identical twist multipliers. Single drops of porcine blood of 2, 10, 30, and 60 µL were allowed to fall 1 cm (to eliminate the impact of blood velocity) onto each fabric to understand the effects of yarn size on wicking and bloodstains. The size of the stain was then measured and compared for different fabrics and blood drop sizes. Wicking of blood into the fabric was fastest for the largest yarn fabrics, but more extensive wicking occurred on finer yarn fabrics resulting in much larger stains. All stains were highly altered due to wicking of blood. The findings from this paper might help the forensic scientists in understanding wicking in textiles and comparing stains on different textiles to gain a better understanding of bloodstains on textiles.

Bloodstain pattern analysis: Does experience equate to expertise?

Bloodstain pattern analysis (BPA) has long been accepted by courts as an area of expertise; however, that position has recently been challenged. The discipline has been criticized for limited empirical research into practitioner determination error rates and whether determinations require specialized knowledge/expertise, including whether practitioner experience level influences accuracy. This study attempted to address these knowledge gaps as they relate to bloodstain pattern recognition. The aims were twofold: to establish whether practitioners would outperform lay non-practitioners, and whether practitioner experience influenced accuracy and error in determinations. Comparisons of practitioner responses under three scenarios (forced, casework, and definitive) were also made to assess conservatism/certainty in pattern recognition. Participants (both BPA practitioners and non-practitioners) analyzed photographs of bloodstain patterns and made determinations of the broad bloodstain category and specific bloodstain pattern type. When forced to provide only a single response, practitioners identified bloodstain categories and patterns significantly more accurately than non-practitioners (p = 0.0001, p < 0.00001, respectively). Practitioner accuracy in bloodstain pattern recognition was positively associated with experience level (p = 0.0429) and this was consistent regardless of response scenario. Although no significant difference in practitioner accuracy was observed across response scenarios, practitioner conservatism/certainty varied significantly among the broad bloodstain category and specific pattern types. Overall, these results support bloodstain pattern recognition as an area of expertise and that practitioner experience positively influences accuracy. Based on these results, a series of recommendations were proposed aimed at further improving practices within the discipline to maximize accuracy and reliability of BPA evidence.

Fundamental study of porcine drip bloodstains on fabrics: Blood droplet impact and wicking dynamics

The underlying physics in bloodstain formation on fabrics is not well understood, despite its importance in bloodstain pattern analysis (BPA). This paper presents a fundamental study of the formation of drip bloodstains on fabrics, by focusing on blood droplet impact and wicking dynamics. The bloodstains were created on plain woven fabric by the perpendicular impact of a single blood drop with seven different impact velocities. The whole droplet impact and wicking processes were captured by multiple cameras. Fabric properties were characterized in detail at different levels. The bloodstain formation process was classified into distinct stages, including the inertial impact, initial absorption, first wicking and second wicking stages. The subsequent wicking process greatly alters the impact-induced bloodstains, in terms of bloodstain area. The dimensionless impact-induced stain factor (β_i,e) is strongly dependent on the impact velocity while the final stain factor (β_f,e) after the second wicking stage is not. The contribution of the subsequent wicking in altering the stain factor (or stain area) is quantified and found to decrease with increasing impact velocity. The blood wicking dynamics on the fabric in the majority of the first wicking stage can be well described by a simple scaling: [Formula: see text] , where t_i marks the end of the inertial impact stage. The wicking coefficient C, which represents the influence of droplet impact on the subsequent droplet wicking, is found to scale as C∼We^-0.34. In the end, brief comments are provided regarding (1) the influence of the evaporation on the blood drop post-impact wicking dynamics and (2) the shape of bloodstains formed on fabrics, with a few suggested research directions for future work.