1 Blood Stain Pattern Interpretation 2 General Features of Bloodstain Formation 3 General Features of Bloodstain Formation 4 General Features of Bloodstain Formation 5 SURFACE TEXTURE Surface texture is of paramount importance in the interpretation of bloodstain patterns arising from blood dripping off an object. Comparisons between stadards and unknowns are valid only when identical surfaces are used. In general, harder and nonporous surfaces (such as glass or smooth tile) result in less spatter. Rough surfaces, such as carpeting or wood, usually result in irregularly shaped stains with serrated edges, possibly with satellite spatter. 6 Smooth surface, no satellite spatter 7 Experiment #1 Surface studies: Vertical Drips on Various Surfaces 8 Direction and Angle of Impact 9 Direction of travel 10 Direction and Angle of Impact 11 12 Determining the Angle of Impact 13 14 Impact Bloodstain Spatter Patterns 15 16 Impact Bloodstain Spatter Patterns 17 Impact Bloodstain Spatter Patterns 18 Impact Bloodstain Spatter Patterns 19 Impact Bloodstain Spatter Patterns 20 Origin-of-Impact Patterns 21 Notice that the lines are drawn in the opposite direction of the direction the blood droplet is traveling. The direction of the spines indicate the direction in which the blood was traveling at the time of impact with the target surface. When a straight line is drawn through the long axis of the stain, they should intersect at some point. This is the area of convergence. Area of Origin: It may also be important to determine the area of origin of a bloodstain pattern, the area in a three-dimensional space from which the blood was projected. This will show the position of the victim or suspect in space when the stain producing event took place. The distribution of the drops in an impact pattern gives a general idea of the distance from the blood source to the blood-stained surface. Impact patterns produced at a distance close to the surface will appear as clustered stains. As the distance from the surface increases, so do the distribution and distance between drops. 22 23 Origin-of-Impact Patterns 24 More Bloodstain Spatter Patterns 25 26 Gunshot Wounds The location of the injury, the size of the wound created, and the distance between the victim and the mussle of the weapon all affect the amount of back spatter that occurs. Finding high-velocity spatter containing the victim’s blood on a suspect can help investigators place the suspect in the vicinity when the gun was discharged. Back spatter created by a firearm generally contains fewer and smaller atomized stains than does forward spatter. A muzzle blast striking an intrance wound is expected to cause the formation of atomized blood. 27 Gunshot Wounds Depending on the distance from the victim at which the gun was discharged, some back spatter may strike the shooter and enter the gun muzzle. This is called the drawback effect. Blood within the muzzle of a gun can place the weapon in the vicinity of the gunshot wound. The presence of blow-back spatter on a weapon’s muzzle is consistent with the weapon being close to the victim at the time of firing. 28 29 Cast-Off Spatter A cast-off pattern is created when a blood-covered object flings blood in an arc onto a nearby surface. This kind of pattern commonly occurs when a person pulls a bloody fist or weapon back between delivering blows to a victim. The bloodstain tails will point in the direction in which the object was moving. 30 31 32 Arterial Spray Spatter 33 Arterial Spray Spatter 34 35 36 37 38 Void Patterns A void is created when an object blocks the deposition of blood spatter onto a target surface or object. The spatter is deposited onto the object or person instead. The blank space on the surface or object may give a clue as to the size and shape of the missing object or person. Once the object or person is found, the missing piece of the pattern should fit in, much like a puzzle piece, with the rest of the pattern. Voids may be applicable for establishing the body position of the victim or assailant at the time of the incident. 39 40 Other Bloodstain Patterns 41 42 43 Flows Patterns made by drops or large amounts of blood flowing by the pull of gravity are called flow patterns, or flows. Flows may be formed by single drops or large volumes of blood coming from an actively bleeding wound or blood deposited on a surface from an arterial spurt. Clotting of the blood’s solid parts may occur when a flow extends onto an absorbent surface. 44 Pools A pool of blood occurs when blood collects in a level (not sloped) and undisturbed place. Blood that pools on an absorbent surface may be absorbed through-out the surface and diffuse, creating a pattern larger than the original pool. This often occurs with beds or sofas. 45 Skeletonization The edges of a stain will dry to the surface, producing a phenomenon called skeletonization. This usually occurs within 50 seconds of deposition of drops, and longer for larger volumes of blood. If the central area of the pooled bloodstain is altered by wiping, the skeletonized perimeter will be left intact. This can be used to interpret whether movement or activity occcured shortly after the pool was deposited, or whether the perimeter had time to skeletonize before the movement occurred. This may be important for classifying the source of the original stain. 46 47 Document!!! Blood spatter patterns of any kind can provide a great deal of information about the events that took place at a crime scene. For this reason, investigators should note, study, and photograph each pattern and drop. This must be done to accurately record the location of specific patterns and to distinguish the stains from which laboratory samples were taken. The photographs and sketches can also point out specific stains used in determining the direction of force, angle of impact, and area of origin. 48 |