When liquid blood is subjected to different physical forces, bloodstains and projected patterns are deposited on various surfaces. Bloodstain pattern analysis (BPA) is based on observation of the shape, size, direction, distribution and dispersal (arrangement) of the bloodstains in order to identify a mechanism of creation. These bloodstains and patterns can provide important information about events that have led to their creation. This information can lead to the reconstruction, in part or in whole, of the sequence of events and/or the assessment of witness and suspect statements.
BPA is a complex process. At a crime scene, the patterns produced by different mechanisms can overlap and therefore exhibit characteristics of different types of bloodstains. The shape and nature of the surfaces studied also affect the appearance of bloodstains. Moreover, the extent and complexity of an event are influenced by the possible movement of the blood source as well as the displacement of objects present at the crime scene.
While the first studies of BPA were published in 1895, research in this field is still a growing discipline of forensic science. Development of new tools and methodologies will further improve the way bloodstain pattern analysts work.