Tulisa. foster Criminalistics I – 7m Instructor: Travis Allen Blood patterns 1. Explain the terms area of convergence and area of origin and explain what each term reveals to an investigator. Area of convergence is a two dimensional plane where lines traced though the long axis of, several individual bloodstains meet. Two dimensional places from which the bloodstains were projected. (saferstein) Area of origin location in three dimensional spaces that blood that produced a bloodstain originated from.
Location of the area of convergence and the angle of impact for each bloodstain is used to approximate this area.
(saferstein) 2. Explain the difference between forward spatter and back spatter and identify which is more likely to be deposited on the object of the person creating the impact. Forward spatter, blood that travels away from the source in the same direction as the force that caused the spatter.
Back spatter is blood that is directed back toward the source of the the force that caused the spatter. saferstein) The back spatter will be deposited on the object of the person creating the impact. (saferstein) 3. Explain what determines the size of blood drops in a cast-off pattern. The size is related to the size of the point from which they was propelled. Drops propelled from a small or pointed surface will be smaller and the pattern is linear. The drops from a larger or blunt surface will be larger and the pattern wider. The volume of blood deposited on an object from the source also affects the size and number of droplets.
How can investigator tell the direction of travel of blood from the shape of a bloodstain? The pointed end of a bloodstain always faces its direction of travel. 5. What is a void pattern? How might a void pattern be useful to investigators? An area within a deposited spatter pattern that is clear of spatter, caused by an object or person blocking the area at the time of the spatter’s deposition. Void pattern can help tell how a victim or assailant body position was at the time of the incident. (saferstein) 6. Name and describe two methods for documenting bloodstain patterns.
The grid method is the first and it involves setting up a grid of squares of known dimensions over the entire pattern using string and stakes. A medium –range and close up photographs are taken with or without the grid. The second method is perimeter ruler it involves setting up a rectangular border of rulers around the pattern and then placing a small ruler next to each stain. This method the large ruler show scale in the overall and medium- range photos, to where the small ruler show scale in the close up photographs. (saferstein) Works Cited saferstein, r. from the crime scene to the crime lab . prentice hall.