FORENSIC IMPLICATIONS OF THE CIRCULATORY SYSTEM Blood found at a crime scene can be used to identify the victim or the perpetrator. Blood type is a class characteristic. – Ex. if the victim had O blood, finding AB blood at the crime scene suggests that the perpetrator had that blood type. Many people may have that blood type, but suspects with any other blood type can be excluded.

FORENSIC IMPLICATIONS OF THE CIRCULATORY SYSTEM Nuclear DNA found in the blood can be used as individual evidence. – Red blood cells do not have a nucleus or DNA. – However, white blood cells have a nucleus and nuclear DNA. – Except for identical twins, each person’s nuclear DNA is unique. Therefore, DNA can be used to identify the victim or the perpetrator.

Blood Blood is biological evidence—it comes from a living or once-living source. When blood evidence is found at a crime scene, investigators ensure the integrity of the evidence through proper collection and evaluation techniques.

Red Stuff when a red stain is found, investigators must ask three basic questions: – Is it blood? – Is it human blood? – If it is human blood, can the blood be traced to a single person?

Hemastix® (for spot stains) presumptive test used to indicate whether the red stain might be blood (Figure 6-8). plastic strips that have been treated with a special blood reagent. – If the stain is blood, the reagent on the test strip turns green. (Iron in hemoglobin acts as a catalyst in this reaction) A catalyst is any substance that speeds up a chemical reaction.

Luminol (for large area of blood): presumptive test— Mixed with hydrogen peroxide. During the reaction with hydrogen peroxide, the luminol is oxidized and light energy is released (see Figure 6-9). – Therefore, the luminol test is viewed in a darkened area.

The Leucomalachite green Presumptive test based on the same reaction in luminol but in the presence of iron: – Leucomalachite green turns blue-green.

Kastle-Meyer test. Presumptive test A solution of phenolphthalein is used, which turns pink in the presence of traces of blood.

Collection of blood evidence: Bag each evidence in a paper bag separately to avoid cross-contamination of the evidence. If the blood evidence is found on a small object, such as a pencil or soda can, the object is packaged and the blood evidence is removed at the lab.

Collection of blood evidence: If the blood evidence is found on a large object, such as a door or wall, only the blood evidence is collected. – Investigators collect dried blood in a variety of ways. wet swab to remove the blood. place fingerprint tape over the blood and lift the stain, use a sharp instrument to scrape blood into a paper bag.

Collection of Evidence Note: Blood needs to be air dried. – Drying the blood prevents mold or other microorganisms from forming. Microorganisms can destroy the evidence. Evidence collected from the suspect acts as a control or known sample.