At a crime scene, bloodstains are the most incredible pieces of evidence. Bloodstain pattern analysis (BPA) might reveal crucial details during and after a crime. Blood spatter analysis allows investigators to identify what transpired at a murder scene and make educated guesses about the victim’s condition. The amount, size, location, and distribution of stains at a crime scene are part of the static aftermath (Zou and Stern, 2022). If a detective is trained to read the signs, the evidence they find in a victim’s blood might be astounding. There are several causes for blood to be left behind, each of which might create its unique pattern. Arterial, directional-angle, drip-trail, cast-off, blowback, saturation-stain, void, smear, swipe, and wipe are only some of the patterns that might occur. The most prevalent causes of bloodstain patterns include force dispersing blood from a point or area source, time dispersed, the volume under pressure, gravity drawing blood, and accumulation or flowing on a surface.
Since droplets always strike a surface the same way, forensics experts can tell in what direction a drop of blood moved. The particle will continue to move in the same direction it was going before it hit the ground. The blood in the droplet spreads outward during the collapse phase, leaving an elliptical or round stain when the droplet hits a surface (Comiskey, Yarin and Attinger, 2019). A forensics expert will examine the bloodstain with other evidence to deduce the blood droplet’s direction of motion. Features like satellite stains, scallops, and spines can also be seen in bloodstains. There will be more of these characteristics on one side of the stain than the other. This is because of the manner the droplet breaks apart when it hits the ground. Spines, scallops, or even satellite stains can form when the dimples on the rim separate minimally from the droplet structure; a bloodstain’s apex always indicates the direction of motion.
A high-resolution photograph is the most reliable method of documenting bloodstain evidence. The size of the bloodstain can be determined by placing a ruler or other measuring instrument close to it and photographing it from all possible angles. Investigators should preserve blood pattern evidence whenever possible (Esaias et al., 2020). If the carpet is soaked with blood, a sample should be collected and taken to a lab for analysis. A sterilized cotton swab or gauze can collect the blood if possible. Keep the swab away from direct sun and moist environments by storing it in a collecting box or a clean, dry envelope.
Understanding a lot about blood reveals that the angle can affect the droplet. A blood droplet, for instance, will create a circular splatter with satellite droplets or spikes all around it if it falls at a 90-degree angle. Moreover, the diameter of a blood droplet lowered from 24 inches is substantially less than a droplet declined from 48 inches (Attinger et al., 2019). The blood droplet will become elongated and have a tail (spikelet) in the route it traveled if it is dropped at an angle of 20 degrees. A droplet’s elongation decreases as its angle of descent approaches 90 degrees. The contour of a 70-degree dip will be more elliptical. One could identify which way the blood was flowing by looking at the spines, which would be more numerous in one direction. Converting the findings of BPA research into innovative, practical, and transparent techniques for homicide investigations and trial presentations is an ongoing issue.
The BPA’s primary function in a criminal investigation is to help reconstruct the sequence of events that could have caused the spots and stain patterns found at a crime scene, on physical evidence recovered, and on clothing found. Bloodstain design translation by photography may be necessary at times. The presence of blood at a crime scene, particularly involving violence, provides the examiner with valuable information about the possible timeline of events between the victim and the offender. Bloodstain patterns at the site or on the clothing of potential principals might be used to confirm or refute hypotheses about the sequence of events (Attinger, De Brabanter and Champod, 2022). The victim’s posture, such as whether they were standing, sitting, or reclining, can be deduced from the bloodstain pattern. The presence of bloodstain patterns can also provide battle corroboration.
Strengths
Recognizing the direction of a phenomenon is essential for pinpointing its convergence point and position of origin. A line drawn through the longitudinal direction of the blood stain will reveal the convergence point. If there is more than one blood stain, analysts connect them with a line. Convergence can be determined by finding the point at which the lines representing the various stains in the sample set meet (Attinger et al., 2019). If investigators can pinpoint the position of the point of convergence, they will have a better idea of where the violence began. Crime scene investigators can use the location of the source to make an educated guess as to the relative positions of the victim and suspect at the time the violence broke out.
The presence of blood at a scene of crime provides investigators with a wealth of information from which to conclude. Examples include variations in the victim’s speed, the crime’s point of origin, and the victim’s angle of impact when the blood was dropped. The analyst can also determine the nature of the object(s) used to create the pattern, the appropriate number of stabs during the incident, and the angle from which the force was applied (Comiskey, Yarin and Attinger, 2019). It is also possible to determine the timing of events, the order in which they occurred, and the relative locations of the perpetrator, the victim, and any relevant objects at the scene. By carefully listening to the patterns of bloodstains, an analyst can effectively reconstruct a crime scene.
The results of a bloodstain design examination can confirm or disprove principals’ versions of events. Wherever their knowledge, education, and experience may be utilized to show that the indictment’s version of events is false, expert witnesses should be considered vital defense team members. BPA enhances the method for examining blood at a crime scene to determine when and what kind of crime occurred. In the study of homicide and other violent crimes where blood is present, it can aid in reconstructing the crime scene. Since the late 1950s, the US criminal justice system has accepted the claims of BPA specialists that they can employ biology, physical science (fluid dynamics), and mathematical computations to recreate what happened at a crime scene accurately. When a bullet leaves a person, for instance, it has already had many jarring interactions with blood and tissue, leading to forward splatter (Attinger et al., 2019). Percolation theory, which explains possible routes through randomly clustered nodes, is applied in blood spatter analysis. In random networks, the movement of clustered elements is described by percolation theory.
Weaknesses
Studies conducted since the 1990s have placed severe doubt on the reliability of blood spatter analysis. BPA is fraught with tremendous ambiguities, and ‘experts’ judgments tend to be more intuitive than scientific (Bettison et al., 2021). Many cases where blood spatter analysts exaggerated their credentials are highlighted, and the validity of their methodologies is called into question. The most comprehensive assessment of BPA’s reliability, released in 2021, found that its findings often differed from those of other analysts and were thus incorrect.
BPA’s capacity to provide credible testimony in court has come under criticism in recent years. This was notable after a study from the National Academy of Sciences concluded that the analysts’ approach lacked scientific rigor and was fraught with significant ambiguity. The report voiced its displeasure with the technique and lack of certification standards for analysts and the prioritization of expertise above scientific rigor (Bettison et al., 2021). Despite the lack of institutional certification or minimum educational qualifications, various bloodstain pattern experts have appeared in court as professionals after having completed a 40-hour course given independently. Even after extensive training and rigorous methodologies, respected analysts often have differing views on findings, casting doubt on their reports’ validity and use as proof in court.
Robust empirical data do not support using BPA in court or elsewhere in the legal system. Some analysts exceed what can be verified when analyzing bloodstain patterns. However, certain components of BPA, such as techniques to identify the impact speeds of scattered blood, may be backed by scientific investigations. The conditions of bloodstain pattern studies, commonly performed at the demand of either the prosecutors or the defense in a courtroom, might incorporate cognitive bias into the analyst’s evaluation. They could also underscore concerns about the basic scientific credibility of the approach (Bettison et al., 2021). Disagreements about BPA language and classifications indicate the need for more precise guidelines. The errors and conflicts resulting from semantic discrepancies and contradicting interpretations can severely impact casework.
Conclusion
BPA may provide crucial information both during and after a criminal act. Blood spatter analysis helps detectives identify what happened at a crime scene and speculate on the victim’s health. Force dispersing blood from a point or area source, moment dispersed, the volume under pressure, gravity drawing blood, and buildup or flowing on a surface are the most common causes of bloodstain patterns. A phenomenon’s convergence point and origin can only be determined if its direction is known. There is a wealth of information for detectives to glean from the presence of blood at a crime scene. There are many unknowns regarding BPA, and ‘experts’ tend to make decisions based on their gut feelings rather than complex data. In recent years, doubts about BPA’s ability to present convincing evidence in court have arisen.
Reference List
Attinger, D., De Brabanter, K. and Champod, C. (2022) ‘Using the likelihood ratio in bloodstain pattern analysis’, Journal of Forensic Sciences, 67(1), pp. 33-43.
Attinger, D., et al. (2019) ‘A data set of bloodstain patterns for teaching and research in bloodstain pattern analysis: gunshot backspatters’, Data in Brief, 22, pp. 269-278.
Bettison, A., et al. (2021). Bloodstain pattern analysis: does experience equate to expertise? Journal of Forensic Sciences, 66(3), pp. 866-878.
Comiskey, P., Yarin, A. and Attinger, D. (2019) ‘Implications of two backward blood spatter models based on fluid dynamics for bloodstain pattern analysis’, Forensic Science International, 301, pp. 299-305.
Esaias, O., et al. (2020) ‘Improved area of origin estimation for bloodstain pattern analysis using 3D scanning’, Journal of Forensic Sciences, 65(3), pp. 722-728.
Zou, T. and Stern, H. (2022) ‘Towards a likelihood ratio approach for bloodstain pattern analysis’, Forensic Science International, 341, p. 111512.
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