May 2005, Page 26
Interpretation Of Blood Spatter For Defense Attorneys - Part Two
By Louis L. Akin
Velocities Of Blood Spatter
There are three classifications of velocities of blood patterns with a large undefined gap between the medium and high speed velocities. This gap is a result of the velocity classifications having grown out of the blood stains found at crime scenes which have limited causes i.e. gravitational pull, blunt instrument acceleration, and super high speed misting as a result of gun shot wounds. The velocity is that of the force causing the blood to move rather than of the speed of the blood itself and it is measured in feet per second (fps); high velocity blood, for instance, may be caused by a bullet moving at 1800 fps.
Low velocity stains are produced by an external force less than 5 fps (normal gravity) and the stains are 3mm and larger.1 It is usually the result of blood dripping from a person who is still, walking, or running, and sometimes from cast-off. Dripping blood often falls at a 90-degree angle and forms a 360-degree stain when it hits a flat perpendicular surface, depending on the texture of the surface. Spines can be caused by drops repeatedly landing in the same place, by the distance the drop falls, or by the surface upon which the blood lands.
Figure 1: Classic 90-degree angle blood drops caused by gravity. The spines were caused by the relatively textured brown wrapping paper. Glass may have produced perfectly smooth edges.
Low velocity blood may also be found in the trail of a person who is bleeding and larger pools of blood may indicate where the person paused.
Figure 2: Low velocity blood from the simulation of a bleeding person walking or running. Note that the blood drops “point” in the direction of travel. The blood is from cows and the surface is brown wrapping paper. These are classic angled drops with waves probably impacted the surface at roughly 60-degrees.
Medium blood spatter is produced by an external force of greater than 5 fps and less than 25 fps.2 The stains generally measure 1-3mm in size. They are often caused by blunt or sharp force trauma That is, knives, hatchets, clubs, fists, arterial spurts, and sometimes cast-off.
Weapon cast-off, or just plain cast-off blood is often found at crime scenes where blunt or sharp instruments were used as the weapons of attack. It is sometimes confused with arterial spurts. Cast-off blood is flung off the weapon — an axe, knife, club — as a result of centrifugal force as the weapon is swung back over the attacker’s head. Cast-off spatter tends to be oval or elliptical in shape as the weapon is being swung through an arc, but becomes more round as it strikes at a 90-degree angle at top dead center over the attacker’s head. It may be classified as low or medium velocity depending on the drop size. See photograph below and Figure 4.3
Figure 3: Cast-off Blood Pattern
Figure 4: Drawing of cast-off blood from the arc of a chopping or stabbing, or clubbing motion. Note the 90-degree round spatter at the top-dead-center position over the attacker’s head.
Arterial blood graphically displays in squirted arcs the pumping of the left ventricle of the heart. As the ventricle contracts, the blood is squirted out of the artery as water from a water pistol. It starts with a low pressure that increases then decreases causing the arcing pulse that results in the distinctive blood pattern. Arterial blood spatter doesn’t lead far because the bleeder looses blood volume quickly and goes into shock or dies; although, occasionally, victims have covered surprisingly long distances while bleeding arterially.
The arterial blood pattern may be confused with cast-off blood patterns or obfuscated by layover patterns. The bleeder may still be under attack while bleeding arterially and may sustain further bleeding wounds or may be bleeding from previous wounds. The arcs are commonly accompanied by bloody handprints and other forms of transfer blood such as swipe and wipe. The bleeder may fall against the blood spatter and smear the pattern (wipe) or smear blood from his or her body or clothing onto the surface (swipe).4 These are but two forms of transfer blood that may confuse the picture at crime scenes and even worse in photographs of crime scenes.
Figure 5: The author simulates arterial spurting on brown wrapping paper. These spurts were produced using a hypodermic needle and cow blood and, while this photograph shows the arc pattern, the amount of blood from actual arterial spurts is usually greater and messier. The arcs may staircase downward as the victim collapses to the floor.
Most medium velocity blood will be in the form of patterns created by blood flying from a body to a surface as a result of blunt and sharp trauma. It may be the result of a punch, stabbing, or a series of blows. In Figure 6 below the author demonstrates how repeatedly punching a blood soaked roll of paper towels can create medium velocity blood spatter the way spatter may be around a person’s head in an actual beating.
Figure 6: Medium velocity spatter as a result of punching a blood soaked roll of paper towels.
In Figure 7, above next page, the pattern can be seen after the roll of towels was removed depicting the way blood spatter leaves a void where the victim’s head was located during the beating. Such a void space may be created by anything that blocks the blood from falling on the surface where it would have landed. The object creating the void may be either the victim or the attacker’s body or a piece of furniture that was moved in order to stage the scene. Locard’s Principle of Exchange states that whenever two objects come into contact some of the matter of each object is transferred to the other. Slightly paraphrased by criminalists, Locard’s principle has become a cardinal principle of crime scene analysis and reconstruction: If a person enters a crime scene and leaves, he leaves something of himself at the scene and takes something from the scene with him. This is an accurate enough rephrasing of the principle to be applied in criminalistics and especially at bloody crime scenes. In many cases, the void is what the attacker leaves, and the blood spatter that would have filled the void is what he, or she, takes away from the scene.
Figure 7: Medium velocity blood void.
High velocity blood spatter is produced by an external force greater than100 fps and the stains tend to be less than 1mm. The pattern is sometimes referred to as a mist. High velocity patterns are usually created by gunshots or explosives, but may also be caused by industrial machinery or even expired air, coughing, or sneezing. In any case, the spatter tends to be tiny drops propelled into the air by an explosive force. High velocity droplets travel the least far because of the resistance of the air against their small mass. In gun shot wounds, the area contiguous to the wound may be showered in a mist of blood spatter and may contain pieces of tissue, but areas further away may not have any blood spatter on them or may only have tissue and blood that accompanied it to the surface that it impacted. Explosions and airline or train crashes leave the most complex blood patterns and will not be dealt with in this article.5 Gunshot wounds, which are far more common in a criminal case will be covered.
Up to a distance of 18 to 24 inches (46 to 60cm) a handgun will leave powder and soot on the surface from which it was fired. Figures 8, 9, and 10 depict the differences in the soot and tattooing left by a Beretta 9mm Model 92F at 3 inches, 6 inches, and 12 inches.
Figure 8: Beretta 9m Model 92F 3 inches from target.
Figure 9: Beretta 9m Model 92F 6 inches from target.
Figure 10: Beretta 9m Model 92F 12 inches from target.
Figure 11: The high velocity gun shot wound leaves a mist like appearance.
Is Blood Spatter Analysis A Science Or An Art?
The term most commonly used to describe the process of examining bloodstains at crime scenes for the purpose of determining what happened to who by whom is blood stain analysis.6 However, the procedure is far more akin to a tracker reading a trail sign than a hematologist working in a lab. The analyst interprets the evidence at the scene just as if it were tracks in the sand. In fact, the analyst uses every item of evidence at the scene, as well as the autopsy reports, the police reports, witness statements, and knowledge that he brings to the scene himself such as knowledge about the dynamics of the behavior of blood, knowledge of guns and ballistics, and knowledge of wounds to the human body. The analyst looks at the evidence, and based on what he sees in the blood spatter patterns and other evidence, makes a pronouncement about what he, or she, believes happened. Seen in this light, blood stain analysis is more of an art than a science and is always open to interpretation.
1. Jams, Stuart H., Eckert, William G., Interpretation of Bloodstain Evidence at Crime Scenes, 2nd Edition, CRC Press 1999. p. 10-11.
2. Bevel, Tom; Gardner, Ross M. Bloodstain Pattern Analysis, 2nd Ed. CRC Press 2002.
3. James, Stuart H., Eckert, William G., Interpretation of Bloodstain Evidence at Crime Scenes, supra.
4. Hueske, Edward E., Shooting Incident Investigation/ Reconstruction Training Manual, 2002.
5. Slemko, J., Bloodstain Pattern Analysis, Tutorial Forensic Consulting, http: //www.bloodspatter.com/BPATutorial.htm.
6. Sutton, Paulette T., Bloodstain Pattern Interpretation, Short Course Manual, University of Tennessee, Memphis TN 1998. n
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