Forensic Blood Spatter Analysis

• Forensics studies blood and blood spatter patterns.

Case Study

• Case #48311 involves the discovery of an apparent homicide.
• The crime scene includes one deceased individual, a gun, and multiple blood stains.
• Information gathered at the scene can help determine where the incident occurred, the height of the perpetrator, the force used, and the number of injuries sustained.

Blood Composition

• Blood is a tissue composed of various cell types, each with a unique structure and function.
• Plasma makes up 55% of the blood and is a fluid suspension that carries nutrients, waste, and proteins.
• White blood cells are immune cells.
• Platelets are involved in clotting.
• Red blood cells transport oxygen and account for 45% of blood volume.

Cellular Identification

• Antigens trigger immune responses
• White blood cells produce antibodies, which are Y-shaped structures, that attach to antigens.

Red Blood Cells

• Red blood cells vary based on the presence or absence of antigens
• Primary function is to transport oxygen.
• Hemoglobin, a protein, contains iron (Fe), which makes blood red.
• Horseshoe crab blood uses copper instead of iron.

Blood Types

• Blood types (ABO) are determined by genetics and are inherited.
• Blood agglutination (clumping) can be fatal.
• The Rhesus (Rh) factor is another antigen type; 85% of humans are Rh-positive.
• Blood type is considered class evidence.
• To determine the percentage of a blood type in a population, convert percentages to decimals and multiply, then multiply by 100 to get the final percentage.
• For example, O- blood (O: .43, Rh-: .15) is found in 6.4% of the population (.43 x .15 x 100%).

Testing

• Luminol reacts with hemoglobin and glows under blacklight to indicate blood presence.
• The Kastle-Meyer test also detects hemoglobin.
• ELISA (Enzyme-Linked Immunosorbent Assay) is an antibody test.

Blood Collection

• If blood is wet, collect it with cotton, allow it to dry, avoid using plastic, and keep it cold if possible.
• If blood is dry, place the item in a paper bag.

Blood Spatter Analysis

• Satellites are secondary droplets.
• Spines are elongated extensions caused by adhesion.
• Cohesion causes droplets.
• Blood spatter direction, impact angle, height, and speed can be used
• Blood spatter analysis can determine the direction of origin, impact angle, height, and speed.
• It can also corroborate witness testimony.

Determining Blood Spatter Direction

• Examination involves finding the area of convergence by observing where lines intersect.

Calculating Impact Angle

• Angle of impact is calculated using the formula: sin-1 (width/length).
• More elliptical blood spatters indicate steeper impact angles.
• Height and speed correlate to diameter and can give clues to the events

Bloodstain Patterns

• Can be used to identify what happened at a crime scene.

Determining Incident Location

• The location can be determined by finding the area of convergence, calculating the impact angle, the tangent of the angle, and measuring the distance to find height.