Blood Spatter The television show Dexter highlights the role of blood spatter analysis in forensics and law enforcement work. Blood spatter analysis can be a cornerstone of crime solving. Rooted in the laws of physics, blood spatter analysis provides a method by which the forensic scientist can recreate a crime scene to provide law enforcement with valuable crime solving tools. Blood spatter can reveal incidents that occurred before, during, and after the crime that might go unnoticed otherwise. The variables that are taken into consideration during blood spatter analysis include velocity, surface tension, and viscosity. Blood has certain physical and chemical properties, which remain relatively constant. Likewise, various types of weapons and human actions have properties that can be analyzed. A combination of these constants can provide a picture of what happened at a crime scene. Each of these issues can help the analyst determine things like what type of weapon was used, where, and when.

Blood spatter is defined as "a grouping of bloodstains," which "composes a blood stain pattern," (Bertino and Bertino). Therefore, a single droplet of blood cannot be considered spatter. Only if the droplet of blood occurs with other drops can blood spatter analysis be performed. Blood spatter analysis is defined as "the examination of the shapes, locations, and distribution of patterns of bloodstains, in order to provide an interpretation of the physical events that gave rise to their origin," (Crime Scene Forensics).

Blood spatter analysis has been used throughout the history of forensic science. As early as 1902, blood spatter classification systems were devised. For example, Bertino and Bertino notes that John Glaister outlined six main patterns of blood spatter. These six patterns remain relevant in blood spatter analysis. One of those patterns is the 90-degree pattern of blood hitting a surface. Another pattern occurs when an artery has been hit. In cases in which an artery has been hit, gushing patterns might be observed on the walls or even on the ceiling. Glaister also identified smears, which are caused by a person...

In the same way that smears are formed, trails of blood may also be formed when the victim moves (Bertino and Bertino).
Blood spatter analysis is based on the most fundamental laws of physics and chemistry. Formation of droplets involves a combination of factors including gravity, cohesion, adhesion, and surface tension (Bertino and Bertino). Some of these properties are related to the chemical structure of blood and its plasma; other properties are related to the blow or force of impact, such as velocity.

The properties of blood itself provide the key data used to perform blood spatter analysis. Blood is "thicker than water" because it is more viscous; viscosity is "a fluid's resistance to flow," and is measured by the Pascal second ("Blood Spatter: Properties of Blood"). The Pascal second is only one way of measuring viscosity, but it does provide a constant and reliable unit for forensics researchers. In addition to being viscous, blood is also cohesive; meaning that droplets tend to bond together if they are close together. Cohesion is observable with other liquids too, including water.

In addition to viscosity and cohesion, surface tension is used in blood spatter analysis. Defined as "the force that pulls the surface molecules toward the center of the liquid," and "the tendency of the surface of a liquid to contract to the smallest area possible," ("Blood Spatter: Properties of Blood"). In the case of blood, the surface tension causes the drop to congeal and settle into a spherical shape or globule as it flies through the air. The surface tension of blood, and its cohesion, is what allows droplets to remain intact as they fly through the air ("Blood Spatter: Properties of Blood"). In other words, surface tension competes with gravity during the time blood is in the air. The force used to displace blood must also be large enough that it can overcome the blood's inherent surface tension; the type of instrument used in the crime will also determine how the blood will react to…