Abstract
Bloodstain pattern analysis can be critical for criminal investigations by providing information on the events that have occurred. Interactions of liquids (such as water and ink) and fabrics have been well studied and therefore provide a foundation to understand the more complex interaction of blood and fabrics. Surprisingly, only a handful of peer-reviewed articles have been published on blood-fabric interactions. Hence, insufficient information is available for interpreting bloodstained fabric evidence and reporting on these findings in court.
Firstly, the effect of storing whole porcine blood with a liquid anticoagulant on the bloodstains produced was investigated. Significant increases in packed cell volume and drop diameter, and significant decreases in drip stain size and spreading ratio were identified during storage of the blood. An exact time period for storing blood with a liquid anticoagulant could not be estimated, but it was established that blood with a liquid anticoagulant should be used within a few days, as blood properties changed over time. Therefore, the recommendation is that studies on drip stain characteristics should include steps to monitor changes in blood properties and stain characteristics over the duration of the experiment.
Secondly, drip bloodstains (passive falling droplets due to gravity) at perpendicular impact (simplified) and inclined impact (complex; 45° and 15°) on apparel fabrics were systematically investigated. Common apparel fabrics (100% cotton plain woven, 100% polyester plain woven, blend of 65% polyester / 35% cotton plain woven, and 100% cotton single jersey knit) that had been laundered for 6, 26 and 52 cycles prior to testing, were used. The relationship between drop impact conditions and stain characteristics was statistically examined to determine the effects of prior-laundering, fibre content and fabric structure on the final appearance of the bloodstains produced. The bloodstain shape ranged from circular to oval for the perpendicular impact angle, to elliptical for the most extreme inclined impact angle (15°). For cotton containing fabrics, the blood spread in all directions along the perimeter of the stain and was accompanied by movement of blood into the fibres. This mechanism was different in comparison to synthetic polyester fibres, which did not absorb liquids. A significant increase in the stain size was observed due to the number of laundering cycles for the blend fabric at all the impact angles investigated. Bloodstain characteristics varied due to both fibre content and fabric structure at all the impact angles investigated. Highlighting the importance of considering the age, the fibre type and the fabric structure before interpreting bloodstain patterns for forensic evidence.
Additionally, in an attempt to better understand the blood-fabric interactions, the micro-morphology of drip stains was examined. The polyester fabric had features that were considerably different from the cotton containing fabrics, and these features were mainly due to the way the blood interacted with synthetic fibre versus natural fibres. No micro-morphological features could be identified to distinguish among the cotton containing fabrics. All cotton containing fabrics did have the presence of blood beads, which was not observed on the polyester fabrics. These blood beads formed due to small individual secondary droplets impacting protruding fibres (i.e., pilling on top of the fabric). The penetration of the satellite stains into the fabric was depended on the size of the stain.
In this Ph.D study, a variety of physical properties of fabrics on the formation of drip bloodstains were investigated and found that the final appearance of these stains is highly complex. The information generated from this research will be a valuable resource for forensic examiners and scientists, as it highlights the importance of considering the age, the fibre type and the fabric structure before interpreting bloodstain patterns on apparel.