Forensic Bloodstain Pattern Analysis PDF

FORENSIC BLOODSTAIN PATTERN ANALYSIS Pick up notes Stamping Helle Crafts Video Questions Blood and Death Blood can be released from a body before and after death (due to gravity) If the blood spatter...

FORENSIC BLOODSTAIN PATTERN ANALYSIS Pick up notes Stamping Helle Crafts Video Questions Blood and Death Blood can be released from a body before and after death (due to gravity) If the blood spatter pattern indicates arterial gushes that is a sign the victim was alive when the wound was inflicted (because the heart was still pumping) Bleeding to death will typically occur after 40% or more of the blood volume is lost (~5 liters) Blood stain can help determine time of death because as the blood dries it oxidizes, but many conditions affect this such as temperature and humidity Wet blood is better because it can be tested for drugs, but it starts to dry as quickly as 3-5 minutes Blood Evidence Blood typing can provide class evidence; whereas DNA profiling can provide individual evidence. A blood spatter pattern can give information about the truthfulness of an account by a witness or a suspect. It also can provide information about the origin of the blood, the angle and velocity of impact, and type of weapon used. Blood Spatter Analysis of a spatter pattern can aid in determining the: ○ direction blood traveled ○ angle of impact ○ point of origin of the blood ○ velocity of the blood ○ manner of death Blood Spatter Too much blood can disguise spatter or make stain patterns unrecognizable. Conversely, too little blood, just one or two drops, will likely yield little or no useable information.  Stains that overlap or come from multiple sources present challenges to analysts, but often reveal valuable details about the crime. DNA profiling can be used when there are multiple victims to determine which spatters belong to which victim Six Blood Spatter Patterns Passive Drops Arterial Gushes Splashes Smears Trails Pools Drops, in general A drop of blood dropped at a 90° angle forms a near-perfect spherical shape When blood falls from a height or at a high velocity, it can form satellite droplets. When it falls onto a less-than-smooth surface, it can form spiking patterns around the drops. Volume Determining Distance (height) Blood Falls Blood Fall Height The higher the drop, the higher the velocity and the larger the diameter. Due to air resistance, speed maxes out at distances above about 7 feet Effect of Surface Directionality of Blood Blood tends to stick to surfaces, so when the blood hits it will leave a thicker spot and trail off into smaller satellites. The area of convergence will be opposite the direction of travel. The TAIL Points to the direction the blood was going! Blood can go in multiple directions in one action Passive Drops Arterial Gushes These are formed when blood falls directly onto a floor at a 90-degree angle.  This produces circular drops, that may have more spikes or satellites depending on the type of surface it is landing on We can determine the height a passive drop feel from because the higher it was dropped the larger the drop will become. These are typically found on walls and ceilings. They are caused by blood spraying out of wound due to the pumping action of the heart These will only occur when a major artery has been cut (veins do not squirt) Splashes Smears Splashes are usually shaped like exclamation points. The shape and position of the spatter pattern can help locate the position of the victim at the time of the attack. These are left when a victim is bleeding and deposits blood as he or she touches or brushes against a wall or piece of furniture. Trails Pools These can be left if a bleeding victim is moving from one location to another or is being moved. Trails can also be left if something is dragged through the blood. These form around a victim who is bleeding heavily and remains in one place. If the victim moves or is moved, there may appear to be droplets or smearing connecting the two locations. Type of Weapon Blood spatter can help determine the type of weapon because the higher the velocity of the weapon the smaller the blood droplets. For example blood from a gunshot wound sprays out in a fine mist, while a wound caused by being struck with a pipe will cause larger drops. Empty space (voids) in the pattern can also help investigators determine where people may have been located in the room at the time of the crime. A Void Pattern Velocity of Blood Spatter  After leaving the body, the velocity blood travels is referred to as low, medium, or high. Low Velocity Spatter The characteristics of a low velocity spatter are the pattern consists of large separate or compounded drops with diameters of 3 mm or more. produced by minimal force and hits the surface with less than 5 ft/s velocity Dripping Blood from a wound. Medium Velocity Blood Splatters The characteristics of a medium velocity spatter consists of small drops with diameters of 1 -3 mm. they travel at an average of 5 to 25 ft/s They are commonly associated with blunt force trauma. Cast Off Patterns A cast-off pattern is created when a blood-covered object flings blood in an arc onto a nearby surface. High Velocity Blood Splatters The characteristics of a high velocity spatter are that it consists of drops with diameters of less than 1 mm. This blood spatter hits at more than 100 ft /s. Gunshot spray. Stain Patterns of Blood A shooting may leave a distinct gunshot spatter pattern. This may be characterized by both forward spatter from an exit wound and back spatter from an entrance wound. WARNING Next slide has a graphic image- Gunshot wound Wound Characteristics The location of injury, the size of the wound created, and the distance between the victim and the muzzle of the weapon all affect the amount of back spatter that occurs. Angle of Impact Splashes help us determine the directionality of the blood and the angle of impact.  We can calculate the impact angle by measuring the length and width of the droplet and using the formula: Sin-1 = width/length After calculating the angles we can use that information to figure out the area of convergence Area of Convergence The location of the source of blood can be determined if there are at least two drops of blood splatter. This can be determined by drawing straight lines down along the axis of the blood spatter and taking into account the angle of impact. Where the lines intersect is the area of convergence. WARNING Next slide has a graphic image- Flow Pattern Flows Patterns made by drops or large amounts of blood flowing by the pull of gravity are called flows. Documenting Bloodstain Evidence Investigators should note, study, and photograph each pattern and drop of blood to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken. Documentation The investigator should create photographs and sketches of the overall pattern to show the orientation of the pattern to the scene. Blood Spatter Experts