|Type of paper:||Research paper|
|Categories:||Forensic science Technology|
Chapter 1: Introduction
1.1 Background of the Study
1.1.1 Definition of Bloodstain Pattern Analysis
Bloodstain Pattern Analysis (BPA) refers to the forensic study of blood formations that are created in crime scenes when there is a bloodletting incident (Connolly, Illes, and Fraser 2012). Analysts of blood evaluate the shapes, the sizes, as well as the locations of the bloodstains which helps them to determine the physical events that may have created them (Li, Li, and Michielsen 2016). Studies have demonstrated that blood patterns can be utilized to ascertain various factors which include the sequence of events, the movement that may have occurred at the scene, the possible type of weapon used, the positions of the victims and the perpetrators, and the area of origin of the incident that led to bloodletting among other factors (Laan, Bruin, Slenter, Wilhelm, Jermy, and Bonn 2015). Therefore, the analysis of bloodstains may be achieved in multiple ways including the direct scene evaluation as well as analysis of photographs (Joris, Denvelter, Jenar, Suetens, Vandermeulen, Van de Voorde, and Claes 2014). For a full report, BPA is done in conjunction with the weapon analysis, cloth analysis, hospital records, lab reports, crime scene reports, and post-mortem photographs, among others.
1.1.2 History of Blood Stain Analysis
Blood Stain Analysis has been considered to be a recent forensic discipline which developed in the mid-20th century (Attinger, Comiskey, Yarin, and De Brabanter, K. 2019). It has been established that BPA was not fully developed as a crime investigation technique in the earlier days (De Castro, Carr, Taylor, Kieser, and Duncan 2016). However, the crime-solving approach can be recognized in the 1890s during the analysis of Polish scientist Dr. Eduard Piotrowski. Before the full recognition of BPA in forensic analysis, it was established that artists, as well as authors, had identified the importance of blood analysis and its pattern in facilitating criminal investigation (Chan and Michielsen 2016. Since then, analysis of bloodstain patterns has been conducted in various criminal investigations which facilitate identification of the criminal activities that had taken place during the event (Bou-Zeid and Brutin 2014).
1.1.3 Blood properties and characteristics
Blood is illustrated loosely as a non-Newtonian fluid. Its viscosity depends on the shear rate while the complexity of the structure as well as the temperamental qualities make blood one of the most difficult substances that concordant information can be obtained from especially when it is applied to the analysis of the blood drops as well as flight characteristics (Goede, Laan, Bruin, and Bonn 2018). Blood contains various elements such as plasma, platelets, white blood cells, and red blood cells, among other substances (Li, Li, and Michielsen 2017). However, the percentages of these substances are not the same for everyone all the time hence depicting the complexity of analyzing a blood sample. Besides, considering that blood does not obey the Newtonian laws, the factors such as viscosity are hard to categorically recognize and analyze (Bremmer, Bruin, van Gemert, van Leeuwen, and Aalders 2012). For example, viscosity values are noted to be influenced significantly by temperature, shear rate, time, and the packed cell volume. Within the field of BPA, experts tend to focus on the analysis of viscosity effects as opposed to the fundamental parameters that may have given rise in the observed effects (Ackerman, Ballantyne, and Kayser, 2010). Therefore, it is imperative to understand the nature and properties of blood to understand the technological applications in Bloodstain Pattern Analysis.
1.1.4 Directional analysis of blood patterns
Directional blood analysis is a mathematical procedure that is used to evaluate the direction of the source from the blood spot identified (Agrawal, Barnet, and Attinger 2017). It has been argued that when viewed from above, the virtual strings demonstrate the convergence onto the source position. Such analogies are based on the laws of motion, including the resolution of velocity into its three trigonometric components. The directionality of the blood drop is essentially determined by the shape of the bloodstain, including the tail, scallops, and the spines (Arany and Ohtani 2011). Therefore, forensic experts have used the analysis of direction to determine the movement that may have occurred at the crime scene at the time of the event that led to bloodletting (Attinger, Moore, Donalson, Jafari and Stone 2013). The other factors that are imperative in the analysis of blood pattern include the area of convergence and the angle of impact (Behrooz, Hulse-Smith, and Chandra 2011). In the area where the individual bloodstains are traced, the area of convergence can be determined in a 2-D size. Additionally, forensic experts evaluate the angle of impact, which is created between the surface and the blood drop. All these techniques including the edge characteristics of blood require the use of technological approaches for accuracy and surety of making inferences regarding the nature of the crime.
1.1.5 Dynamics and age analysis
Dynamics under the influence of velocity, wettability of surface and viscosity of blood plays a critical role in the interpretation of bloodstains due to its subsequent influence towards the efficiency and reliability of bloodstain analysis. Dynamics impact on the area of blood spatter and may alter their point of origin due to the interaction of bloodstains with various surfaces (i.e. surface tension raised between two materials of distinct physio-chemical structure). The chronology of events leading to the proper inferences based on crime scene information will help to determine how the various technologies are used simultaneously in a manner that they effectively complement each other. Some of the technologies are not only useful in determining the area of origin of the bloodstains based on the morphology of the blood spatter pattern, but also enables the investigators to determine the approximate age of the bloodstains to provide an interpretation of when, where and how the physical events took place (Camana, 2013; Dror et al, 2012; Edelman et al., 2012; Hakim and Liscio, 2015).
The documentation of bloodstain evidence is an essential first step that requires high-scale resolution photography. DNA profiling tools are also employed to identify the perpetrator of a crime. The interpretation of patterns obtained from a crime scene is a vital stage in the bloodstain pattern analysis. In general, the events that make up a proper bloodstain pattern analysis are categorized into pattern analysis and reconstruction, and with appropriate technologies, the two can be addressed efficiently (Camana, 2013; Dror et al, 2012; Edelman et al., 2012; Hakim and Liscio, 2015).
Several technological methods as follows have been developed in bloodstain pattern analysis to provide valuable insight in determining bloodstain formation on different types of surfaces, in terms of the impact angles, point of origin and drop volume etc. According to Taylor, Laber, Kish, Owens, and Osborne (2016) and Buck et al. (2011), there is need for improved technological models, such as 3D technology models (Figure 1) that has been used to determine the approximate ballistic trajectories of the drop by taking gravity and drag forces into consideration to prevent overestimation of deposition height up to an average of 50% (Figure 2) (Behrooz, Hulse-Smith and Chandra, 2011; Attinger et al., 2013) and provide useful clues regarding the origin, victim position, approximate number of blows, and event sequence leading to a crime.
Ballistic determination of bloodstains trajectories and origin was performed using the Ballistic Software. The Ballistic Software presents a high accuracy of the analysis of bloodstains by using blood drops to approximate trajectories. Photogrammetry software determines the areas of origin of the bloodstains. Virtual Stringing is another software employed in their research simplifies trajectories into straight lines for the blood that has dropped on flat ground. It relates both the horizontal and vertical orientation of the blood stains. Tachymetry is a theodolite that employs an electro-optical laser distance measuring approach to determine the spatial or terrestrial location of blood drops and converts the measurements into 3D CAD software (ArchiCAD, AutoCAD 2006, etc.).
Hakim and Liscio (2015) studied the application of laser scanning technology in establishing the point of origin relating to an impact pattern as compared to other virtual stringing software. In their study, the accuracy and the reproducibility of the point of origin estimation was determined using the FARO Scene Software with FARO Focus laser scanner. The overall results attained from 15 blood spatters gave a SD = 3.49 cm (p < 0.0001) in the xdirection, SD = 1.14 cm (p = 0.9291) in the ydirection, and SD = 9.08 cm (p < 0.0115) in the zdirection, in which these results are more accurate than other virtual stringing software (i.e. BackTrack and HemoSpat). Furthermore, Table 1 presented the results attained from the Mann-Whitney tests, in which increment of the displacements in x and z coordinates were observed as the distance between the front wall (i.e. x direction) and impact origin gets further. Whereas, changes of the x direction did not have significant influence in the y coordinate due to the lack of influence of the travel distance.
Another study by Agrawal, Barnet, and Attinger (2017) proposes simulations and experiments for quantifying the uncertainty on the impact and directional angles. In this method, fabric properties are fed into a numerical model to determine the size and velocity of the bloodstain after impacting of the blood droplet on both porous and non-porous fabric. However, stains on porous fabric (i.e. a hydrophilic substrate) are less explored because of the effect of imbibition dynamics (i.e. capillary transportation of liquid caused by the wetting forces and the resistance of viscous forces) in the fabric after the impact, which causes the deformation and amplification of the bloodstains, hence measurements errors occurred in determining the directional and impact angles. In other words, the spreading behaviour of the bloodstain is due to the interpolation between capillary regime and viscous regime as expressed in equation 1 (Laan et al.,2015).
Wmax/Do= Re1/5 p1/2sina(A+P12sina45) ..........Eqn (1)
where P is the impact number determined by P = WeRe- 25 and A = 1.24
Besides dynamics, age of the bloodstain or known as post-mortem intervals is key to the determination of the timing of a crime, which depends on the drying rate of bloodstains and its volume (Laan et al, 2016). Hence, there is a need for a more consistent and accurate approach using advanced technologies to realize the estimated bloodstain age.
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