Blood Spatter Analysis Area of Convergence Learning Goal

Blood Spatter Analysis: Area of Convergence Learning Goal: How can the shape of blood help scientists understand where the blood originated?

Goals: 1. Distinguish between blood-spatter droplets and blood-spatter satellites. 2. Distinguish between passive blood spatter and blood spatter that was emitted due to some type of force 3. Use the shape of blood droplet to determine the direction in which a drop of blood was moving 4. Use the position of satellites to determine the direction in which a drop of blood was moving. 5. Use blood spatter to draw the lines of convergence to indicate the position where a person was located when bleeding occurred.

Materials: - 1 ruler - 1 colored pencil - 1 pencil

Scenario: When the police arrived at a crime scene, both the victim and the attackers had already fled. Two areas of blood spatter were the only evidence that an assault had occurred. After drawing lines from the blood spatter, the crime scene investigator determined not only the direction the blood spatter was traveling and the approximate speed the blood was traveling but also the approximate location where the person was standing when the injury occurred. Blood-spatter analysis can help investigators can help reconstruct what happened at a crime scene. When you enter a crime scene, there is always a story waiting to be discovered. An observant crime-scene investigator doesn’t always need eyewitnesses to describe what happened, because the scene always tells the story. You can use blood-spatter analysis to reconstruct what happened at a crime scene.

Scenario: In this activity, you will analyze blood spatter. By noting the direction of the droplet of blood, you will be able to note the direction in which the blood was moving. The size of the blood spatter will provide some indication of the velocity of the blood when it hit a surface. By examining at least two droplets of blood spatter, you will be able to determine where the injured person was located when the injury occured. When blood-spatter analysis is completed and theses factors are determined, it may be possible to reconstruct what happened at the crime scene.

Background: The shape of an individual drop of blood provides clues to the direction from which the blood originated. A drop of blood that has a circular shape (equal width and length) indicated that the blood fell straight down. When blood falls straight down, such as when it drips from a wound, the angel of impact id 90 degrees. This type of blood spatter is known as passively produced, because no applied force caused the spatter. When a drop of blood is elongated (longer than it is wide), it is possible to determine the direction the blood was traveling when it struck a surface. The location of the source of blood can be determined if there at least two drops of blood spatter. By drawing straight lines down the long axis of the blood spatter and noting where the lines intersect, this will indicate the lines of convergence. To determine where the source of the blood originated, draw a small circle around all of the intersecting lines. The intersection of the lines of convergence will indicate in a two-dimensional view the location of the source of the blood.

Procedure: 1. For each of the four different blood-spatterns pictured, you will draw lines of convergence to determine the source of blood. 2. Determine the direction in which each blood spatter is moving. a. Locating the tail of the blood spatter and any satellites. 3. Draw a line through the middle of the long axis. 4. Draw the line in the opposite direction from the direction in which the blood was traveling. 5. Draw a small circle around the point where all of the lines intersect. This is the source of the blood or area of convergence. 6. For each of the four samples, determine how many incidences occurred.

Describe what could have happened in sample A? - How many individuals are involved? Explain - In what direction is movement? Explain

Describe what could have happened in sample B? - How many individuals are involved? Explain - In what direction is movement? Explain

Describe what could have happened in sample C? - How many individuals are involved? Explain - In what direction is movement? Explain

Describe what could have happened in sample D? - How many individuals are involved? Explain - In what direction is movement? Explain

Questions: 1. Indicate which of these blood-spatterns (sample A, B C, or D) represents bleeding from: a. A bullet wound that causes bleeding as the bullet entered the body and as the bullet passed through the body of one individual Sample(s) _________ because _________________________________________ __ b. Two separate instances of bleeding, possibly from two different individuals Sample(s) _________ because _________________________________________ __ c. A single wound from one individual Sample(s) _________ because