A blood pool at a crime scene is a collection of blood on a surface that results from substantial bleeding. These pools are a significant source of information in real-world forensic science. They are considered passive stains because they form from the force of gravity rather than from the force of an impact. An investigator’s analysis of a blood pool can provide information about the physical events that occurred.
The Formation of a Blood Pool
A blood pool forms when a source of blood remains stationary over a level and undisturbed surface for a period. The resulting size and shape of the pool are heavily influenced by the properties of the surface it forms on.
On non-absorbent surfaces like tile or sealed concrete, blood will spread out, its shape dictated by surface tension and the volume of blood. The edges of such pools are often raised due to the cohesive forces within the blood. In contrast, absorbent surfaces like carpet or fabric will wick the blood away from the initial point of contact. This absorption alters the final shape and size of the visible stain and can separate the blood solids from the liquid serum.
Information Revealed by Blood Pools
The characteristics of a blood pool offer numerous insights for forensic investigators. The extent of drying and clotting can act as a timeline. The drying process occurs in stages, which can help estimate the time elapsed since the blood was deposited. For instance, the separation of yellowish serum from the clotted red cells is dependent on the volume of blood, ambient temperature, and time.
The volume and overall shape of the pool can suggest the original position of a victim or a bleeding object. Patterns within and around the pool are also revealing. A void, or an area within the pool that is free of blood, may indicate that an object was present during the bleeding and later removed.
Another pattern is skeletonization, which is the dried outer ring of a bloodstain that remains after the center of the pool has been disturbed. This can show that the source of the blood or another object was moved after bleeding had started but before the entire pool had dried. These patterns help investigators reconstruct the sequence of events at a scene.