bloodstain

A bloodstain is the mark left when blood is deposited on a surface. It can result from passive dripping, contact between a bloody object and a surface, or high-velocity impact. The appearance of a bloodstain depends on factors such as the surface type (porous or nonporous), the volume and velocity of blood, the angle of impact, and environmental conditions like temperature and humidity. Fresh stains are bright red and become darker as they dry; on porous materials blood can wick and spread, while on nonporous surfaces it may maintain more defined edges.

In forensic contexts, bloodstains are categorized by pattern. Passive stains include drips and flows produced by gravity, while transfer stains arise when a bloody object contacts a clean surface. Spatter patterns result from impact or projection and can inform investigators about the source’s location and movements. The geometry of stains—directionality, concentration, and distribution—helps reconstruct events, though interpretations must account for surface properties and post-depositional changes.

Preservation and analysis involve documentation, collection, and testing. At scenes, stains are photographed and mapped before collection by swabbing or cutting for laboratory analysis. Presumptive tests, such as luminol, may reveal blood not visible to the naked eye, while confirmatory tests determine blood origin (for example, human versus animal) and enable DNA analysis. Results are interpreted with caution and in conjunction with other evidence.

Limitations include alterations from cleaning, environmental exposure, or multiple incidents, which can complicate pattern interpretation. Bloodstain analysis is a supplementary tool in crime scene reconstruction and forensic investigations, providing clues about events but not by itself providing precise timings or unequivocal sequences.