Forensic Science Lab Activity T. Trimpe 2006 Warning: Some material in this presentation and related videos may be too graphic for some people.
What does the abbreviation BPA represent? Bloodstain Pattern AnalysisWhat can an investigator learn from the analysis of a blood spatter?Type and velocity of weaponNumber of blowsHandedness of assailant (right or left-handed)Position and movements of the victim and assailant during and after the attackWhich wounds were inflicted firstType of injuriesHow long ago the crime was committedWhether death was immediate or delayedHow does a blood droplet form? Click the image for an animation.Source: -analysis1.htm
Light SourceInvestigators will first examine the crime scene to look for areas that may contain blood. They may use a high-intensity light or UV lights to help them find traces of blood as well as other bodily fluids that are not visible under normal lighting conditions. How is blood evidence detected at a crime scene?Blood Reagent TestsThese tests, referred to as presumptive tests, are used to detect blood at crime scenes based upon the properties of hemoglobin in the blood. Further tests at the crime lab can determine if it is human blood or not.Examples:•Phenolphthaleinis a chemical that is still utilized today and is usually referred to as the Kastle-Meyer test and produces a pink color when it reacts with hemoglobin. •HemaStixis a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or blue-green color with the presence of Kastle-Meyer TestVideoHemaStix
LuminolThis chemical is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed. Investigators spray a luminol solution is throughout the area under investigation and look for reactions with the iron present in blood, which causes a blueluminescence. One problem is that other substances also react, such as some metals, paints, cleaning products, and plant materials. Another problem is that the chemical reaction can destroy other evidence in the crime scene. Luminol ReactionLCVor Leuco Crystal Violet, is one type of chemical process that is used for blood enhancement. Using this test helps to make the blood evidence more visibleso it can be photographed and analyzed.