Blood Analysis and Blood Spatter

1. Blood Analysis and Blood Spatter Bronx Community College Chemistry Department Summer 2009 Forensic Science Workshop Monica Ye- Bard High School Early College & Lilliana Mendoza-Bronx Center for Science and Math Nature of Blood Identifying Blood Confirmatory Test: Blood Spatter & Blood Stain Analysis: Blood is a mixture of cells, enzymes, proteins, and inorganic substances. The fluid portion of blood is called plasma, which is mostly contains nutrients and dissolved proteins. The cellular phase of the blood contains red blood cells, white blood cells, and platelets. There are three different blood types: A, O, and B. To identify the blood type scientist have to have a specific anti-body that will match up with the blood antigen. After the presumptive test the blood sample needs to undergo another procedure that will confirm the presence of blood. -The confirmatory test is also known as the Takayama test. The Takayama test will confirm if the substance found at the crime scene is blood or something that looks like blood. A sample of the blood is placed on a slide and examined under a microscope: a) if the substance found is blood crystal-like shapes will form. b) if the substance is NOT blood no crystal like shapes will form. Substance found at the crime scene is not a 100% blood, a preliminary or screening test procedure is used to determine if the substance is blood, this procedure is called Presumptive Testing. -Presumptive Testing is based on the reactivity of hemoglobin, a protein found in red blood cells that carries oxygen throughout body . Two different chemicals are used in this test: Phenolphthalein and O-toluidine. When Phenolphthalein is used the blood sample will turn a pink-purple color. When O-toluidine is used the blood sample will turn a green-blue color. Blood spatter is a group of blood stains resulting from one or more injuries. Spatters are produced in different ways; such as stabbing, gunshots, beatings, cast-off blood, and splashing. Careful study of these spatters can help forensic scientists to figure out: -the origin of the blood stains -type of weapons used -the direction which the object struck the victim -movements of the victim and the suspect -the number of hits the victim received -sequence of events There are three basic types of blood stains found at a crime scene: Importance of Blood • Blood contains DNA. DNA contains the genetic material, this can be used to determine who was at the crime. • Blood can be used to determine the sequence of how a crime occurred. • Blood found at a crime scene can be used to determine what kind of weapon is used at the crime scene. • Blood can also help identify the origin of the blood. Under the microscope if the substance found at the crime scene is blood, crystals like the one shown on the right will form under the microscope - Passive: are blood drops created or formed by the force of gravity alone. - Transfer: is created when a wet, bloody surface comes into contact with another surface. - Projected: are created by more force or action greater than gravity. Angle of Impact: Phenolphthalein turning pink due to the reactivity of hemoglobin found in blood The light portion of the tube is called plasma phase. The darker portion is the Cellular phase. -When a blood drop is dropped from a 90 degree angle, the drop is round and the length as well as the width would be equal. -When blood falls at an angle less than 90 degrees, its shape would resemble a teardrop. -The pointed end of the blood stain is called the “tail” and it would always point in the direction of the travel of the blood. This is a diagram showing different blood drops that fall from different angles. Acknowledgements: • Dr. John Molina • Dr. Sat Bhattacharya • Bronx Community College • National Science Foundation • Harlem Children Society • Harlem Children Society Staff