Types of Blood Spatter Stains
The size, shape, location, and distribution patterns of blood stains found at a crime scene can help to determine the sequence of events, the approximate locations of blood sources, the position of the victim, the type of weapon used, intensity and number of impacts applied to the blood source, etc.
FORMATION OF BLOOD STAINS
Blood stains are formed when blood leaks out from a source and comes in contact with another object. Blood falling through the air takes the shape of a sphere. However, the formation of bloodstains is influenced by a lot of factors including the angle of impact, velocity of the weapon, type of surface impacted, and other surfaces that may have come in contact. This can lead to the formation of a variety of blood stain patterns found at a crime scene which can be mainly categorized as passive, transfer, and projected blood stains.
1. Passive blood stains
Passive blood stains are formed when blood is deposited on a surface by the influence of gravity alone. They can be further classified into:
Figure: Passive Blood Stain Patterns (Drip, Splash, Flow, Pool, and Serum stain)
Drip stain: A drip stain is formed when blood from a wound or an object drops on a surface. Eg: blood dripping from a finger, or blood dripping from a knife covered in blood. A trail of drip stains (drip trail) is formed if the source of blood (a wounded individual or object covered in blood) is moving while the blood is dripping. If the source of blood is not moving, multiple drops of blood fall into each other at the same spot, forming creating a drip pattern.
Splash pattern: A splash pattern is formed when a volume of blood spills onto a surface. Splash patterns usually consist of large blood stains surrounded by many small and elongated stains.
Flow pattern: A flow pattern is caused by the directional movement of blood on a surface due to gravity. The direction of the flow will always be downwards (towards the ground) due to the effect of gravity. The direction of the flow can help us determine if the body or object was moved after the crime.
Pool: A pool is a bloodstain formed by the accumulation of blood on a surface. Pools are formed when a large volume of blood collects on a leveled surface (like floor) that is not sloped. Eg: A victim shot dead on the floor will create a pool around the body due to a large amount of blood leaking from the wound. The approximate drying time of a pool can help the investigators in approximating the amount of time that has passed since the blood was deposited and when it was found, i.e. the time when the crime took place.
Serum stain: A serum stain is formed when serum (the liquid portion of the blood) separates after coagulation. These stains are almost transparent with a reddish colour around the boundary.
2. Transfer blood stains
A transfer bloodstain is created when a blood-bearing surface comes in contact with another surface, leaving an impression on the previously unstained surface. Transfer blood stains can be further divided into:
Figure: Transfer Blood Stain Patterns (Contact, Swipe, and Wipe)
Contact pattern: A contact bloodstain is formed when a bloody object comes in contact with a previously unstained surface, without any movement. The edges of a contact bloodstain are clean and usually look like a bloody impression has been stamped on a surface. Eg: A murderer steps in a pool of blood and walks away from the room, leaving a contact blood stain pattern of their shoes. The shape, size, and distance between these impressions can point toward the direction as well as the speed of the individual, along with additional information like shoe size, height, etc. The blood stain patterns will start to get lighter as the individual moves away from the source of blood, and the distance between two consecutive patterns increases or decreases depending on the speed.
Swipe pattern: A swipe pattern is formed when a blood-bearing surface in motion comes in contact with another surface that was previously unstained, thus, leaving a smudged impression. These impressions can provide information about the shape, size, and pattern of the blood-bearing object. One side is usually feathered which indicates the direction of travel. Eg: A murderer hastily touches the wall with his bloody hands as he walks away. The swipe patterns created can provide more information about fingerprints, palm prints, the direction in which the murderer was going, etc. that may aid in investigations.
Wipe pattern: A wipe pattern is formed when an unstained object passes over a pre-existing wet blood stain and alters its appearance. Eg: A murderer pulls the body of a victim across a blood-stained floor, creating wipe patterns on the floor. Examination of wipe patterns may inform the investigators about the motion and direction of the object.
A perimeter stain is a type of wipe pattern that has been disturbed before it is fully dried but it maintains the peripheral characteristics of the original stain. Such stains are created because the edges of the blood stain dry faster than the center.
3. Projected blood stains
Projected bloodstains are created when a volume of blood is deposited on a surface under a pressure or a force that is greater than the force of gravity. Projected blood stains can be further divided into:
Figure: Projected Blood Stain Patterns (Impact pattern, Cast-off pattern, Expiration pattern, Arterial sputter, and Void pattern)
Impact pattern: An impact bloodstain pattern is a type of bloodstain pattern that is created by the force of an object, such as a blow, striking a surface and causing the release of blood from an injury. Eg: Someone was struck with a blunt object, such as a baseball bat, on the head. The force of the impact would cause blood to be released from the injury and create droplets of various sizes that would be projected outwards in various directions. The droplets could create an ‘impact pattern’ of stains on nearby surfaces, such as a wall or floor, which could be used to determine the location and direction of the impact. Additionally, the size and shape of the stains could be used to estimate the force of the impact and reconstruct the events that occurred.
Cast-off pattern: is formed when blood drops are released from a moving blood-bearing object such as a weapon or an injured person's hand. These droplets can travel a significant distance from the source and create a pattern of stains on surfaces in the area. These patterns are commonly seen in injuries caused by a projectile. A forward spatter is formed when blood drops travel from an exit wound in the same direction as a projectile, while a back spatter is formed when blood drops travel from an entry wound in the opposite direction of a projectile. The pattern of stains can be used to determine the direction and speed of the movement of the person at the time of injury, and can also provide information about the type of weapon used and the distance between the shooter and the victim.
Figure: Formation of Cast-off stains
Expiration pattern: An expiration pattern is formed when blood is expelled out of the nose or mouth resulting from an internal injury in the chest or throat, or when a person is suffocated. These blood stain patterns are often lighter in color as they get diluted with saliva, and contain air bubbles. The blood droplets created by expiration can only travel a short distance from the source. So, expiration bloodstain patterns can be found on surfaces near the victim, such as walls, floors, clothing, or on the face and neck of the victim. The size and shape of the stains can provide information about the breathing rate and effort at the time of injury, which can help determine the cause of death. The location and direction of the stains can also provide information about the position of the victim at the time of injury.
Arterial sputter: An arterial sputter results from blood being forced out of an artery under high pressure, typically seen in cases of knife or sharp object attack where the weapon has struck a major artery. The blood droplets created by the spurt are often fine, mist-like, and can travel a significant distance from the source. Instead of a constant flow, spurts of blood will be released with fluctuations with each heartbeat. The pattern of stains can be used to determine the location of the injury, as well as the direction of the spurt. This information can be useful in reconstructing events that occurred at a crime scene. Eg: if an arterial spurt pattern is found on a wall, it can indicate the position of the victim and the attacker at the time of the injury, as well as the direction of the attack. Additionally, the size and shape of the stains can be used to estimate the force of the spurt, which can provide information about the severity of the injury.
Void pattern: A void pattern is created when an object blocks the deposition of blood stains on a surface. The blood stains are deposited on the object instead. When the object is removed from the surface, a characteristic pattern can be seen where blood is absent (void) similar to the shape of the object, surrounded by continuously distributed bloodstains.