Blood Spatters

Bloodstain pattern analysis is the interpretation of bloodstains at a crime scene in order to recreate the actions that caused the bloodshed. Blood spatter analysis can tell the distance from the source of the blood to the pattern, the direction from which the blood impacted, the speed the droplet was traveling, the location of the point of origin, and even the movement of a bleeding individual throughout the scene.
There are three basic types of bloodstains. The first type of bloodstains are passive stains which include drops, flows, and pools. Drops fall at ninety degrees and are spherical. Flows result from movement of volume of blood on a surface due to gravity. Pools result from an accumulation of blood on a surface. The second type of
bloodstains are transfer stains which include wipes, swipes, and pattern transfers. Wipes are altered bloodstain patterns resulting from an object moving through a pre existing wet bloodstain. Swipes result from the transfer of blood from a blood-bearing surface onto another surface. Pattern transfers result from contact between a blood-bearing surface and another surface. The third and final type of bloodstains are projected or impact stains which include splashes and arterial spurts. Splashes result from a volume of liquid blood that falls or spills onto a surface. Arterial spurts result from the severing of a major blood vessel where each beat of the heart sprays out more blood.
One of the ways you describe the characteristics of blood spatter are by the speed at which blood leaves the body, which is called velocity.
The three types of velocity are low, medium, and high velocity spatter. Low velocity spatter is 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 four millimeters 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 about four feet. Medium velocity is 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 around two to four millimeters. The force associated with this type of spatter is greater than twenty-five feet per second. High velocity spatter is impact spatter that measures less than two millimeters in diameter. The force necessary to produce high velocity spatter is greater than one hundred feet per second. This type of spatter is usually associated with gunshots, explosions, and high speed collisions and looks very
misty.
The other way you describe the characteristics of blood spatter are by type of force applied to the blood source.
The three types of force are sharp force, blunt force, and a gunshot. Sharp force is caused by an object with a relatively small surface area such as a knife or ice pick. There is less blood deposited on the weapon which means there is a smaller, more linear pattern of stains. Blunt force usually deals with larger objects such as a baseball bat or a piece of firewood which is one of the weapons used in this case. The larger surface area of the weapon will collect more blood than that of an object used to produce sharp force which will produce drops of varying sizes. Gunshots produce a misty spatter which is made by bullets entering and exiting the body. This includes both forward spatter from the exit wound and back spatter from the entrance wound. Voids occur when a person or object blocks the path of the blood and they can tell if something has been removed from the scene or if another person was
present.
There are five steps to determining the point of origin of blood. In step one you have to determine direction of blood and mark with arrows next to drops. If the drops are circular, blood was dropped at 90 degrees. If the drop isn’t circular, the tail the of blood drop points to the direction in which blood was moving. In step two you look at several drops of blood, determine the area of convergence by drawing lines through each of the blood droplets and drawing a circle around where the lines intersect. In step three you have to measure the distance from the area of convergence to the edge of the blood drop where it first hit the surface. In step four you must determine the angle of impact for each droplet of blood. The arcsine of width/length of the drop is the angle of impact, width being the shorter measurement. In step five you use the Law of Tangents to solve for height. Step four gives us the angle, step three gives us the length of the adjacent side, and now, in step five, we solve for the height which is the opposite side.