User:Alind123/Bloodstain pattern analysis

Bloodstain pattern analysis (BPA) is a forensic discipline focused on analyzing bloodstains left at known, or suspected crime scenes through visual pattern recognition and physics-based assessments. This is done with the purpose of drawing inferences about the nature, timing and other details of the crime. At its core, BPA revolves around recognizing and categorizing bloodstain patterns, a task essential for reconstructing events in crimes or accidents, verifying statements made during investigations, resolving uncertainties about involvement in a crime, identifying areas with a high likelihood of offender movement for prioritized DNA sampling, and discerning between homicides, suicides, and accidents.

The International Association of Bloodstain Pattern Analysts (IABPA) serves as the primary organization for professionals in the field, while the method of bloodstain pattern analysis is commonly referred to as BPA. Since the late 1950s, BPA experts have claimed to be able to use biology, physics (fluid dynamics), and mathematical calculations to reconstruct, with accuracy, events at a crime scene, and these claims have been accepted by the criminal justice system in the US.

Grounded in principles of physics, biology, chemistry, and medicine, bloodstain pattern analysts use a variety of different classification methods. The most common classification method was created by S. James, P. Kish, and P. Sutton, and it divides bloodstains into three categories: passive, spatter, and altered.

Despite its importance, classifying bloodstain patterns poses challenges due to the absence of a universally accepted methodology and the natural uncertainty in interpreting such patterns. Current classification methods often describe pattern types based on their formation mechanisms rather than observable characteristics, complicating the analysis process. Ideally, BPA involves meticulous evaluation of pattern characteristics against objective criteria, followed by interpretation to aid crime scene reconstruction. However, the lack of discipline standards in methodology underscores the need for consistency and rigor in BPA practices.

Efforts by organizations like the Organization of Scientific Area Committees (OSAC) BPA Subcommittee aim to establish standards for training, terminology, quality assurance, and procedure validation within the discipline.

The validity of bloodstain pattern analysis has been questioned since the 1990s, and more recent studies cast significant doubt on its accuracy. A comprehensive 2009 National Academy of Sciences report concluded that "the uncertainties associated with bloodstain pattern analysis are enormous" and that purported bloodstain pattern experts' opinions are "more subjective than scientific." The report highlighted several incidents of blood spatter analysts overstating their qualifications and questioned the reliability of their methods. In 2021, the largest-to-date study on the accuracy of BPA was published, with results "show[ing] that [BPA conclusions] were often erroneous and often contradicted other analysts."

Acceptance as valid evidence in United States courts[edit]

Between 1880 and 1957, courts in Michigan, Mississippi, Ohio, and California rejected expert testimony for bloodspatter analysis, generally holding that it added nothing to the jurors' own evaluations of bloodstains submitted as evidence. In 1957, the California Supreme Court became the first American court to accept expert testimony examining bloodstains, accepting as evidence the testimony of Paul L. Kirk, a professor of biochemistry and criminalistics. He would also testify in the Sam Sheppard case in 1966, when the wife of an osteopathic physician was beaten to death in her home, interpreting bloodspatter evidence as proof that the murderer was left-handed (Sheppard was right-handed). However, bloodstain pattern analysis would not begin to enter wide use until it was promoted by Herbert Leon MacDonell. MacDonell researched bloodstains with a grant from the United States Department of Justice, and which also published his research in the book "Flight Characteristics and Stain Patterns of Human Blood" (1971). MacDonell testified in court on multiple occasions as an expert of bloodstain analysis, and the legal precedent set by these cases led to its widespread use in American courts, although as early as 1980 some judges expressed strong doubts about its reliability, and it was not always accepted as evidence, especially in states with no prior rulings that relied on such evidence.

The first formal bloodstain training course was given by MacDonell in 1973 in Jackson, Mississippi. MacDonell taught workshops on how to conduct bloodstain analysis, and the newly trained bloodstain analysts, who often had received as little as 40 hours of instruction, in turn would give expert testimony in court cases. In 1983, the IABPA was founded by a group of blood stain analysts to help develop the emerging field of bloodstain pattern analysis.

Bloodstain Types

A bloodstain can present itself differently depending on the situation and the material on which it appears, and bloodstains may be hard to examine on porous surfaces such as fabric, and may be distorted. Bloodstain pattern analysts consider the angle of impact to determine its origin and the amount of force behind it; variations in external forces can cause satellite drops. A point of origin can be determined by finding what bloodstain analysts call the "area of convergence" for the blood droplets. To find this point of origin, the shape of the blood and the length are often taken into account and the stringing method is implemented. In the stringing method, blood drop paths are depicted as straight lines. Strings are placed at the bloodstain positions and pulled away from the surface to reconstruct the direction of impact. This direction is determined by the shape and orientation of the bloodstains. The point where most strings intersect is considered the estimated location of the blood source. There is also a method known as the tangent method. In this method, the blood drops' paths are seen as right-angled triangle hypotenuses. This works best for fast-moving drops with flat trajectories, but uncertainties in their curvature may lead to errors in determining the blood source's horizontal position."

Additionally, the angle of impact as well as other external factors such as the material on which the blood falls can change the shape and size of the blood. The point of impact can change the shape of the bloodstain. Bloodstains, instead of maintaining their original forms, may become elongated. In these cases, the blood may have a tail capable of indicating directionality. In order to find the angle of impact investigators measure the length and width of the blood droplet and use the formula . The (A) representing angle of impact.

Bloodstain Patterns

Impact spatter is the most common bloodstain pattern type in a crime scene. It occurs when an object hits a source of blood. These patterns typically manifest as circular shapes rather than elongated forms. There are two types of impact spatter, back spatter and forward spatter. Back spatter occurs when blood is projected back at an attacker, while forward spatter is blood that exits directly from the victim's wound and projects onto nearby surfaces.

The speed of the weapon used in the attack can cause changes in the size of blood spatter. The speed of the attack is classified into high, medium and low velocity attacks. High-velocity spatter (e.g., gunshot wounds) create small-sized droplets. High-velocity spatter usually travels 100 feet per second and creates blood droplets sized 1 millimeter or less. Medium-velocity spatter (e.g., blunt force trauma) is often made with a weapon and can create cast-off patterns. They are often made at between 5 and 25 feet/second the blood droplets ranging from 1 to 4 millimeters in length. Low-velocity spatters are usually created just as a result of blood dripping from the individual (i.e., gravity).

They can also be referred to as passive/gravity bloodstains (bloodstain patterns that are formed under the influence of gravity), and are separated further into four categories: transfer/contact stains, flow artefacts, drop stains, and pooling. Transfer stains occur when two surfaces come into contact and at least one has blood on it, and it includes swipe and wipe patterns, which can give information regarding sequence of movement in some cases. Pooling occurs when the source of the bleeding remains static for a certain period of time, the blood continuously dripping in the same location and resulting in an important accumulation. If the individual who is actively bleeding moves while blood is dripping, the resulting pattern will allow for determination of direction and relative speed of movement at that time.

Cast-off patterns are associated with impact spatter. These patterns arise from blood being ejected from a bloodied or bleeding object during its movement, commonly observed in incidents involving physical assaults or strikes. They are commonly observed on ceilings when objects are swung overhead, although they can potentially appear on any surface within the surrounding area. These patterns may be used to guess the direction of a weapon swing. In these cases, the length and the shape of the bloodstain patterns can help determine the speed of the swing. These patterns create elongated or elliptical shapes in blood when it hits the surface of an object. In 1895, Dr. Eduard Piotrowski's experiment showed that these patterns are often created after the second hit using the weapon. In some cases, void or shadow patterns can be observed. It is the result of a person or an object shielding an area from the blood coming toward it, and it is characterized by a clean area where bloodstains are expected. It can help determine if whatever intercepted the blood has been moved since the incident occurred.

The rest of the bloodstain types that don’t belong in any of the previously mentioned categories are called altered bloodstains. This includes blood clots and diluted blood.