Blood is one of the most common and important types of physical evidence present at a crime scene. When liquid blood is acted upon by external physical forces, that blood is often distributed through the air in the form of droplets, with bloodstains and bloodstain patterns deposited on adjacent surfaces. Using the mathematical relationship that exists between the blood droplet and resultant bloodstain’s length and width ratio, the angle at which the blood droplet impacted the receiving surface can be determined. Using this relationship, it becomes possible for Bloodstain Pattern Analysts to determine the three dimensional Region of Origin for the blood source from which the bloodstains under examination have originated. A Bloodstain Pattern Analyst performs angle of impact calculations from bloodstains for the purpose of making a three dimensional determination of blood source Region of Origin. The reliability of that determination is based on an assumption that one of the most important biological properties of blood; the amount of red blood cells or hematocrit value, has no influence over the length to width ratio of a bloodstain. As a consequence the Impact angle = arcsine [width/length] calculation has been assumed accurate regardless of the 'unknown' hematrocrit value. This thesis investigated the effect of the hematocrit value on the angle of impact calculation and thus the ability to determine the three dimensional blood source Region of Origin. Bloodstains were created by releasing a series of 18μL droplets, with ten different hematocrit values, onto a ceramic tile at four different angles. The resultant bloodstain length and width was measured and impact angle calculated. Evaluation of the research data shows that the hematocrit value significantly affects the bloodstains length and width. However, it is apparent that there is close agreement between the known and calculated impact angles irrespective of the hematocrit value.
|Publication status||Unpublished - 2009|