Recognition of Bloodstain Patterns
History of Bloodstain Use Over 550 research articles have been written concerning bloodstain patterns and their use for solving violent crimes. n These articles date back to London in the year 1514. n The use of bloodstain patterns as a forensic discipline in the modern era dates back to 1955, when Dr. Paul Kirk submitted findings related to bloodstain evidence in the case of State of Ohio v. Samuel Sheppard. n
Properties of Blood n Biological properties - Blood serves as a transport system for oxygen, nutrients, hormones, antibodies and vitamins. - Blood consists of a fluid portion called plasma, which contains cellular components like red and white blood cells and platelets. - When blood clots, the liquid portion is referred to as serum.
Properties of Blood Red blood cells (erythrocytes) transport oxygen from the lungs via the arteries and return carbon dioxide to the lungs via the veins. n White blood cells (leukocytes) assist with defense against foreign substances and infection. The nuclei of these cells are the sources of DNA in the blood. n Platelets are the main components of the clotting mechanism. n
Other blood properties Total blood volume in healthy adults ranges from 4. 5 to 6. 0 liters. n Physical properties - Blood acts as in a predictable manner when subjected to external forces. - It is held together on the molecular level by strong cohesive forces that produce a surface tension within each drop on the external surface. n
Other blood properties Surface tension is defined as the force that pulls the surface molecules towards its interior. This causes a decrease in surface area and a resistance to liquid penetration. n The shape of blood drops in air, like other liquids, is a spheroid, not tear drop shaped as rain is represented. n The size of the drop will vary depending on the surface area from which the blood drop originated. n
Other blood properties The diameter of a bloodstain produced by a free falling drop of blood is a result of the volume of the drop, the texture it impacts, and to a certain point, the distance it falls. n Once it falls past 7 feet, the shape of the drop does not increase appreciably in diameter. n The volume of an average blood drop is 0. 05 m. L. n
Target surface n n In order to create smaller blood droplets, a force must be applied that disturbs the surface tension. Forces such as gravity and air resistance are not great enough to affect the surface tension of the blood. n n Generally, a hard, smooth, nonporous surface will produce little if any spatter. Rough textures like wood or concrete will produce a significant amount of spatter.
Directionality of Travel n n By examining the edge characteristics of stains, the direction of flight prior to impact may be determined. The narrow end of an elongated bloodstain usually points in the direction of travel. n After the directionality of several bloodstains has been determined, an area or point of convergence can be established.
Area of Origin The area of origin is the location in threedimensions and can also be determined. This requires the determination of impact angles. n If the angle of impact is 90 degrees, then the resulting bloodstain will generally be circular in shape. n
Blood Drops at an Angle n n n Elliptical bloodstains are the result of a bloodstain that strikes a surface at an angle. A mathematical relationship exists between the width and length of these stains. The ratio produced is less than one and the angle can be determined by taking the sine of that number.
Classifying Bloodstains n n n Based upon the correlation between the velocity of the object striking the blood and the size of the patterns. 1) Low-velocity impact spatter 2) Medium-velocity impact spatter n n 3) High-velocity impact spatter There are two broad categories: 1)Results from direct impact 2)Results from an impact that results in satellite or secondary spatter
Types of Spatter n n Misting, or minute spatters less than 0. 1 mm in diameter, are only associated with gunshot wounds. Satellite spatter is created by blood dripping into blood. n Castoff patterns are created by repeated blows to the same area, where blood has accumulated. When the object is swung during these repetitions, blood is flung to nearby objects.
Types of Spatter n Arterial Bloodstain patterns vary from a large gush to a small spray, depending on the amount of damage to the carotid artery. n Expirated bloodstain patterns result from blood being forcefully expelled from the nose, mouth, or lungs.
Castoff n Castoff is blood that has been released or thrown from a blood bearing object. This may result from the repeated striking of a victim with an object. n Once the blood has pooled, it is transferred to the object, so it can then be flung in direction of the swing.
Passive Transfer n n Passive bloodstains are drops of blood created by the force of gravity acting alone. Therefore, the surface texture determines the extent of spatter.