Bloodstain pattern analysis

Bloodstain pattern analysis (BPA), one of several specialties in the field of forensic science, inolves the study and analysis of bloodstains at a known or suspected violent crime scene with the goal of to helping investigators draw conclusions about the nature, timing and other details of the crime. The use of bloodstains as evidence is not new; however, the application of modern science has brought it to a higher level since the 1970s and '80s. New technologies, especially advances in DNA analysis, are available for detectives and criminologists to use in solving crimes and apprehending offenders. The science of bloodstain pattern analysis applies scientific knowledge from other fields to solve practical problems. Bloodstain pattern analysis draws on the scientific disciplines of biology, chemistry, mathematics and physics. If an analyst follows a scientific process, this applied science can produce strong, solid evidence, making it an effective tool for investigators, although care does need to be taken when relying on bloodstain pattern analysis in criminal cases. A report released by The National Academy of Sciences calls for more standardization within the field. The report highlights the ability of blood spatter analysts to overstate their qualifications and the reliability of their methods in the court room. History: Bloodstain pattern analysis has been used informally for centuries, but the first modern study of blood stains was in 1895. Eduard Piotrowski published a paper entitled "On the formation, form, direction, and spreading of blood stains resulting in blunt trauma at the head." A number of publications describing various aspects of blood stains were published, but his publication did not lead to a systematic analysis. LeMoyne Snyder's widely-used book Homicide Investigation (first published in 1941 and updated occasionally through at least the 1970s) also briefly mentioned details that later bloodstain experts would expand upon (e.g., that blood dries at a relatively predictible rate; that arterial blood is a brighter red color than other blood; that bloodstains tend to fall in certain patterns based on the motion of an attacker and victim). The second modern origin of the study of bloodstain pattern analysis is the Sam Sheppard case in 1954, when the wife of an osteopathic physician was beaten to death in her home. Further growth of interest and use of the significance of bloodstain evidence is a direct result of the scientific research and practical applications of bloodstain theory by Herbert Leon MacDonell of Corning, New York. His research resulted in his publication of the first modern treatise on bloodstain analysis, entitled "Flight Characterisics and Stain Patterns of Human Blood" (1971). The first formal bloodstain training course was given by MacDonnel in 1973 in Jackson, Mississippi. In 1983, the International Association of Bloodstain Pattern Analysts was founded by a group of blood stain analysts to help develop the emerging field of bloodstain pattern analysis. Blood: Blood is a tissue that is circulated within the body to assist other parts of the body. This connective tissue has specialized cells that allow it to carry out its complex functions. For a healthy person, approximately 8% of their total weight is blood. For a 70 kg (154 lb.) individual, this equates to 5.6 L (12 US pints). Biological considerations: Blood contains three components or blood cells that are suspended within plasma. The three components are erythrocytes, leukocytes, and platelets. Erythrocytes, also known as red blood cells, are transporters. The role of erythrocytes is to transport oxygen. To do this, they contain great quantities of hemoglobin, which carry oxygen molecules and give blood its distinct red colour. Blood that has passed through the heart and been oxygenated (oxygenated blood travels through the arteries) tends to have a brighter shade of red as opposed to blood that is returning to the heart (in the veins). There are about 30 trillion erythrocytes circulating in the human blood at any given time. Leukocytes, also known as white blood cells, are the body's defenders. The role of leukocytes is to defend against harmful bacteria, viruses and microorganisms. There are five different types of leukocytes. They all have different sizes, shapes, structures, and functions. Leukocytes fight infection and disease. There are about 430 billion leukocytes circulating in the human blood at any given time (~1 per 700 erythrocytes). Pus is made up of leukocytes left in an affected area during and after fighting harmful substances or organisms that infect the body. Platelets are formed in the bone marrow. These particular blood cells contain cytoplasm and are enclosed by a membrane, but do not have a nucleus. They play a major role in hemostasis (control of bleeding) by plugging up a breach in a vessel. They are important for forming blood clots. If a person has an abnormally low platelet count, a condition known as thrombocytopenia, blood clots more slowly. Plasma is the yellowish fluid that carries the erythrocytes, leukocytes, and platelets. It is composed of water (92%), proteins (7%), and other materials such as salts, waste, and hormones, among others. Many of these proteins are clotting factors, which are important along with platelets for forming blood clots; clotting factor deficiencies can cause prolonged and excessive bleeding, a condition called hemophilia. Plasma makes up about 55% of blood. The remaining 45% is the blood cells. Because plasma is less dense than the blood cells, it can be easily separated. Plasma does not separate from blood cells whilst circulating in the bloodstream because it is in a constant state of agitation. Chemical considerations: Upon exiting the body, bloodstains transit from bright red to dark brown, which is attributed to oxidation of oxy-hemoglobin (HbO2) to methemoglobin (met-Hb) and hemichrome (HC). The fractions of HbO2, met-Hb and HC in a bloodstain can be used for age determination of bloodstains and can be measured by Reflectance Spectroscopy 1. In vivo hemoglobin molecules are mainly present in two forms: one without oxygen, de-oxyhemoglobin (Hb) and one saturated with oxygen, oxy-hemoglobin (HbO2), both have iron in the Fe2+ state. HbO2 can auto-oxidize into met-Hb, which contains iron in the Fe3+ state. Met-Hb is incapable of binding oxygen. When met-Hb is formed in vivo it will be reduced back to Hb by reductase protein cytochrome b5, resulting in a small part (<1%) of met-Hb in a healthy in vivo situation. Outside the body hemoglobin saturates completely with oxygen in the ambient environment to HbO2. Due to a decreasing availability of cytochrome b5, necessary for reduction of met-Hb, the transition of HbO2 into met-Hb will, in contrast to inside the body, no longer be reversed. Once hemoglobin is autooxidized to met-Hb it will denature to hemichrome (HC), which is formed by an internal conformation change to the heme group. Physical considerations: In physics there are two continuous physical states of matter, solid and fluid. Once blood has left the body it behaves as a fluid and all physical laws apply. Gravity acts on blood (without the body's influence) as soon as it exits the body. Given the right circumstances blood can act according to ballistic theory. Viscosity is the amount of internal friction in the fluid. It describes the resistance of a liquid to flow. Surface tension is the force that maintains the shape of a drop of liquid, such as blood. When two fluids are in contact with each other (blood and air) there are forces attracting all molecules to each other. Blood spatter flight characteristics: Experiments with blood have shown that a drop of blood tends to form into a sphere in flight rather than the artistic teardrop shape. This is what one would expect of a fluid in freefall. The formation of the sphere is a result of surface tension that binds the molecules together. This spherical shape of blood in flight is important for the calculation of the angle of impact (incidence) of blood spatter when it hits a surface. That angle will be used to determine the point from which the blood originated which is called the Point of Origin or more appropriately the Area of Origin. A single spatter of blood is not enough to determine the Area of Origin at a crime scene. The determination of the angles of impact and placement of the Area of Origin should be based on the consideration of a number of stains and preferably stains from opposite sides of the pattern to create the means to triangulate. Determining angles of impact: As mentioned earlier, a blood droplet in freefall has the shape of an oscillating sphere. Should the droplet strike a surface and a well-formed stain is produced, an analyst can determine the angle at which this droplet struck the surface. This is based on the relationship between the length of the major axis, minor axis, and the angle of impact. A well-formed stain is in the shape of an ellipse (see figure 1). Dr. Victor Balthazard, and later Dr. Herbert Leon MacDonell, realized that the width-length ratio of the ellipse is the sine of the impact angle. Accurate measurement of the stain thus allows easy calculation of the impact angle.