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Forensic Science 4-U Unit: Blood Spatter Analysis Crime Scene Forensics, LLC Examining and Documenting Blood Stain Patterns Bloodstain Pattern Analysis: is the examination of the shapes, locations, and distribution of patterns of bloodstains, in order to provide an interpretation of the physical events that gave rise to their origin. The following Information may be obtained from a proper Bloodstain Pattern Analysis: 1. Distance from the blood source to the target 2. Direction of travel and impact angles 3. Nature of the force used to cause the bloodshed 4. The object used to cause the bloodshed 5. Sequencing of multiple bloodshed events 6.Interpretation of contact or transfer patterns When properly documented, bloodstain patterns found at the crime scene, or on a particular person's clothing, can be used to: 1. Confirm or refute the position of a victim, witness, suspect, or defendant 2. Determine if there is evidence of a struggle, or if the assault is "one sided" 3. Confirm or refute statements made by principles in the case: IE: Are stain patterns on a particular person's clothing consistent with accounts given by the victim, witness, or defendant? Blood Flight Characteristics: Blood will not break up unless it is acted upon by force. The force must be great enough to overcome the surface tension of the blood. Blood forms a spherical shape (perfect circular shape) almost immediately upon separating from the blood source. The spherical shape is caused by the surface tension of the blood. Surface Tension causes the blood drop to pull itself in; both horizontally and vertically. The blood drop will settle into a spherical shape, as a result of the surface tension. The surface tension will maintain the sphere shape of the blood drop until it impacts with the surface. 1 Forensic Science 4-U Unit: Blood Spatter Analysis SPATTER VS TRANSFER: The simplest type of blood spatter analysis is determining spatters from transfers. Spatters are created when blood is acted upon by force, and travels through the air before landing on a target surface. Transfers occur when a blood source comes in direct contact with a target surface area. TARGET SURFACE TEXTURE: Bloodstains can occur on a variety of surfaces. The type of surface that free falling blood strikes affects the appearance of the resulting spatter. Blood drops on a rough surface will make an irregular shaped stain with rough or jagged edges. IMPACT SPATTERS: are random patterns of spatter of varying sizes 2 Forensic Science 4-U Unit: Blood Spatter Analysis LOW FORCE (VELOCITY) IMPACT SPATTER/PASSIVE DROPS: Blood that falls at the speed or force of normal gravity These spatters usually fall from an open wound, or from a surface that is saturated with blood The majority of the Low Force Impact Spatters are large, circular, spatters with diameters of 4mm or more Low Force Impact Spatters will increase in size as the distance fallen increases, however, the size of the spatters will remain constant after approximately 4 feet MEDIUM FORCE (VELOCITY) IMPACT SPATTER: OR PROJECTED SPATTER Produced with more energy or force than gravity The force of the impact causes the blood to break into smaller size spatters relative to the amount of force applied This type of spatter is usually seen in blunt force, stabbings, and secondary spatters Produced when the majority of larger drops of blood are broken into smaller spatters with diameters of 2 – 4 mm The force associated with this type of spatter is greater than 25 ft. per second HIGH FORCE (VELOCITY) IMPACT SPATTER: It is important to note that the term "Velocity" does not measure the speed at which the blood is traveling, but rather is used to describe or measure amount of force applied to the blood, to cause it to spatter. Impact spatter that measures less than 2mm in diameter The force necessary to produce this size spatter is greater than 100 ft. per second This type of spatter is usually associated with gunshots, explosions, and high speed collisions High Force Impact Spatter takes on a "mist like" appearance If the bullet exits its target, a larger amount of high force impact spatter may be directed in the same direction as the bullet. This is known as "forward spatter". The closer to the target that the gun is fired...the great the spatter. 3 Forensic Science 4-U Unit: Blood Spatter Analysis DIRECTION: The "tail" points in the direction the blood drop is traveling. ANGLE OF IMPACT: The steeper the impact, the more elliptical or elongated, the blood drop Measure the width and the length of the stain/spatter sine= width = 9mm length = 18mm 9 divided by 18 = 0.500 Arcsine 0.500 = 30 degree angle of impact Do not measure the “tail”, it is a secondary force or event. Divide the smaller number by the larger number Reference: Crime Scene Forensics, LLC. (n.d.). Interpreting Bloodstain Patterns. Retrieved October 17, 2011, from Crime Scene Forensics: http://www.crimescene-forensics.com/Blood_Stains.html 4