Bloodstain pattern analysis (BPA) is a forensic science discipline dealing with the physics of blood and assesses bloodstain left at crime scenes. The bloodstains are analysed according to the shape, size, and pattern of distribution. BPA can help reconstruct the events at a crime scene, verify statements where doubt of a crime occurring is present, clarify cases where there is doubt whether a crime happened, identify areas with high likelihood of offender movement, and differentiate homicide, suicide, and accident.
A bloodstain pattern refers to the individual spatters which were generated by an impact. Individual spatters will radiate away from the impact source when force is applied on a blood source. The most common idea regarding liquids in flight is that the liquid takes the form of a teardrop. However, a liquid only takes a teardrop form when it drops from an object. Once a drop is in the air, it takes its minimal surface area and moves in flight in a spherical shape. Various physical forces act on liquids in air such as gravity and air resistance. This results in the difficulty of analyzing the cause of bloodstains. Knowledge on physics and BPA is then essential in order to make accurate assessment of what happened in a crime scene
Information from Bloodstain
1. Distance of blood source
2. Type of injuries
3. Direction of travel and impact angles
4. Nature of the force used to cause bloodshed
5. Object used to cause bloodshed
6. Sequencing of bloodshed event
7. Interpretation of contact or transfer patterns
Types of Bloodstains
1. Passive stains – includes drops, flows and pools that typically resulted from gravity
2. Transfer stains – resulted from objects coming into contact with existing bloodstains and leaving behind patter transfers
3. Impact stains – includes those blood projecting through the air and are usually seen as spatter
How BPA is done?
1. Documentation of bloodstain evidence – records bloodstains from crime scenes, usually through photographs.
2. Pattern analysis and reconstruction – looks at the physical characteristics of the stain pattern, identify what type of pattern is present and what may have caused it, reconstruct events and explain the stain patterns
3. Sampling bloodstain for DNA profiling