Picture this: you walk into a crime scene and the first thing you see is blood. It is all over the walls, the floor, and even the ceiling. Now any other person would probably not know the information that this evidence holds, but those that have studied blood, how it works, bloodstain patterns, and what they all mean, have an abundance of evidence to examine. Just from looking at the bloodstain patterns, they can discover many things about the crime and how it occurred.
There are five main categories of bloodstains: passive, impact spatter, transfer, other, and latent. Many of these categories also have sub-categories.
Passive stains are influenced by gravity. Passive stains include drips, splashes, flows, and pools. Drips, or drops, can show how far the blood fell from the source. Depending on the size and shape of the drip, the distance and angle the blood fell from can be determined. Also, if the suspect or victim moves throughout the crime scene and leaves a drip trail pattern, their movements can be established. Splashes come from blood dripping into blood. Splashes can lead to flows. Flows are created when accumulated blood flows from one area to another, being pulled by gravity. The flow direction shows movement from the blood source. If the flow is interrupted, this interruption can show the time that passed between the flow and its interruption. Pools can result from flows. A pool occurs when blood collects on a flat surface. If the blood source is on an absorbent surface, the blood will be absorbed and will spread out and create a larger pattern than the original pool.
Impact spatter stains come from the impact between an object and the blood source. Impact spatter can be separated into three classifications, low-velocity, medium-velocity, and high-velocity spatter. Low-velocity is created by a force traveling at five feet per second or less and produces large blood drops with a diameter of four millimeters and up. These drops are usually from an open wound or a blood saturated object. Medium-velocity impact spatter comes from a force traveling five to twenty-five feet per second, producing drops one millimeter to four millimeters in diameter. Medium-force spatter can come from things like blunt force and stabbings. High-velocity is generated from a force traveling at one hundred feet per second, or faster, and result in drops being one millimeter or smaller in diameter. These spatters are seen with gunshots, explosions, and high speed collisions.
Wipes, swipes, and contact/pattern transfer stains are all in the transfer category. A wipe occurs when a clean object moves through blood. An example of a wipe would be the suspect trying to clean the blood up with a clean towel. A swipe is a result of a bloody object moves across a clean surface and transfers blood. An example of a swipe would be the suspect wiping their bloody knife onto their pants. A contact/pattern transfer stain occurs when a wet bloody object touches another...