Unit 5: Serology 5.2 INTRODUCTION TO BLOOD SPATTER

Unit 5: Serology 5.2 INTRODUCTION TO BLOOD SPATTER

Unit 5: Serology 5.2 INTRODUCTION TO BLOOD SPATTER What is Blood Spatter? Bloodstain Pattern Analysis: is the examination of the shapes, locations, and distribution patterns of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin. Based on the premise that all bloodstains and bloodstain patterns are characteristic of the forces that have created them. FBI website

What do we use blood spatter for? The determinations made from bloodstain patterns at the scene or from the clothing of principals in a case can be used to: Confirm or refute assumptions concerning events and their sequence: Position of victim. (standing, sitting, lying) Evidence of a struggle. (blood smears, blood trails) n Confirm or refute statements made by principals in the case: Are stain patterns on a suspects clothing consistent with his reported actions? Are stain patterns on a victim or at a scene consistent with accounts given by witnesses or the suspect?

FBI website Documentation of Blood Spatter At a crime scene, the blood spatter patterns are photographed and sketched before the blood is collected so that the suspects account can be proved or disproven. The photographs will allow for an interpretation and reconstruction of what happened. Medium Range Photographs: shows the whole pattern and the relationships between individual stains within the pattern.

Close-Up Photographs: show the dimensions of individual stains and should be taken with a scale apparent in the photograph. Methods of Documenting Blood Stains Grid Method Strings and stakes are used to create squares of known dimensions over the entire pattern. Photographs are then taken with and without the grid. Perimeter Ruler Method: A rectangle border of rulers is made around the pattern to

show the overall scale in medium range photographs Small rulers are placed next to each stain to show the scale in the close up photographs. Factors that can help reconstruct the scene Surface Texture: Harder and Nonporous surfaces (glass, smooth tile) result in less spatter. Rough surfaces (concrete floor, wood) result in irregularly shaped stains with serrated edges, possible satellite spatter. Finding the Origin of Impact Helps determine where the blood was projected from-shows the position of the victim or

suspect when the even took place Can also determine how many times an object came into contact with the source of blood Factors that can help reconstruct the scene Shape and Directionality of blood splatter Shape of the mark where it lands reveals the direction in which the drop was traveling and the amount of force it was projected with. Established from the geometric shape of the bloodstain. Classifying the type of blood spatter pattern Can help investigators to determine what type of weapon was used, if the victim was moved, where the suspect went after the crime, if objects were moved during the crime,

etc. Factors that can help reconstruct the scene Size of blood splatter The smaller the drop the faster the movement of the blood. Classifying the type of blood stain The most common type of blood stain pattern found at a crime scene is impact spatter. This type of pattern occurs when an object comes into contact with a source of blood. Forward Spatter: spatter projected outward and away from a source Back Spatter: spatter that consists of blood projected backward from a source potentially being deposited on the object or person creating the impact.

Classifying Impact Splatter We classify the type of impact spatter by looking at the velocity with which a blood drop moves. Velocity is the speed at which something travels with a direction. Low-velocity impact splatter (LVIS) Caused by low-speed impact or force to a blood source. o Examples: gravity alone, minimal force, an object dropping into and splashing blood from a blood pool.

Velocity may be up to 5 feet per second or 1.5 meters per second. Large separate or compounded drops with a diameter larger than 4 millimeters. Classifying Impact Splatter Medium-velocity impact splatter (MVIS) Caused by medium-speed impact or force to a blood source. o Examples: Blunt force trauma, beating or a stabbing. Velocity is about 25 feet per second or 1.5-7.5 meters per second. Drop size or stain of 1-3 millimeters.

Classifying Impact Splatter High-velocity impact splatter (HVIS) Caused by high-speed impact or force to a blood source. o Examples: Gunshot, explosive devices, a cough or sneeze. Velocity may be 100 feet per second or 30 meters per second. Drop size is a mist like appearance forming drops <1 millimeter. Using droplet size is a useful tool that give investigators an insight into the general nature of a crime but it cannot give specifics.

Blood stain analysis should include observations of stain size, shape, location, and distribution to accurately reconstruct what happened.

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