Lim Jason Serology Lab Write Up October 19, 2010
Blood evidence is documented through the use of photography, video and crime scene sketches. With recent technology, there are computer programs that can sketch crime scenes and the user is able to input blood spatter points to calculate points of origins. Blood evidence collection varies depending on the state of the blood. All blood evidence should be labeled with the collector's initials along with a date and time, and also a description of the evidence. The method of collecting blood varies based on the blood's condition. For wet blood, the evidence can be collected by cotton swabs or other absorbent materials. The item used to extract the blood is then placed in an open tube for it to air-dry. Wet samples should not be collected in air-tight containers since it degrades faster than if it is air-dried; if sealed in a container, the sample must be delivered in less than two hours. Refrigeration also keeps the sample intact until it reaches the lab. Dry blood is easier to collect than wet blood. If possible, the blood can be scraped off with a scalpel or knife and collected into a paper packet. If an object is stained with blood, then it is best to send the object itself to the lab instead of gathering blood off of it. If sending the entire blood stained object is not an option, then investigators cut a smaller portion off to test. When investigators suspect that the crime scene was cleaned up, luminol is a solution to reveal the hidden blood. Luminol reacts with any iron, so it reacts with the invisible blood's hemoglobin. If any blood is revealed, the investigator will photograph and record where it is at. Visible blood is preferred over hidden blood, as luminol can dilute or even ruin the blood as evidence. Such solutions are a last attempt to find blood. The forensic importance of analyzing blood and blood stain patterns is that they tell what type of crime occurred. With the collection of blood comes the collection of DNA as well. The blood stain patterns can reveal things like the severity of the attack and the positions of the assaulter and his or her victim.
http://www.crime-scene-investigator.net/blood.html http://books.google.com/books? id=cAylmhNc8UkC&pg=PA209&lpg=PA209&dq=wet+blood+collection+crime+scene&source=bl&o ts=Wuj_6i1kWB&sig=nCSaclp_CfXjW3iYDUmrHEak4wg&hl=en&ei=BWCTJpFkaidB9KSzYkO&sa=X&oi=book_result&ct=result&resnum=3&ved=0CB8Q6AEwAg#v=onepag e&q=wet%20blood%20collection%20crime%20scene&f=false http://www.suite101.com/content/chemiluminescent-luminol-a38625 http://science.howstuffworks.com/bloodstain-pattern-analysis.htm
A case involving blood evidence is Rihanna and Chris Brown.The evidence of Chris Brown's alleged assault on Rihanna focuses not only on the physical damage on Rihanna's face, but also includes the dress that she wore during the attack. The conflict occurred in Brown's rented Lamborghini, where he beat and choked her until she was unconscious. Police took Brown's car and Rihanna's dress because they both had bloodstains on them. They most likely tested to see if it matched Rihanna's blood.
http://www.exposay.com/v/28013/rihannas-bloodstained-dress-presented-evidence-case-against/
There are several presumptive tests to determine whether a red substance is blood at a crime scene. With luminol, blood produces light because the solution reacts with the blood's hemoglobin. The Kastle-Meyer test is a mixture of phenolphtalein and hydrogen peroxide that reacts with the blood's hemoglobin, resulting in a pinkish color. The microcrystalline tests involve adding specific chemicals to interact with the blood's iron to form crystals. Leucomalachite tests interact with blood's the heme group to form a green color. While all these tests can determine if the substance is blood, it is not advisable to perform a test on limited amounts of blood, since it is best for the lab to use the substances rather than the investigator waste it in trying to find out that it is blood. In determining human blood from animal blood, human blood has red blood cells with no nucleus, a smaller white blood cell count, and a moderate amount of platelets. Blood typing is still useful in forensics to exclude suspects based on their blood type. Along with excluding, it can help further build one's case for a particular individual. With the advances in DNA testing, it is more preferable and more accurate to match DNA from a blood sample than trying to come up with a blood profile. DNA, or genetic fingerprinting, is useful in forensic science due to its ability to create a individual characteristic as opposed to a class characteristic from the blood profile. Genetic testings also establish paternity and other family relationships. Blood stain measurements at a crime scene does not need to be exact, but rather need to be a rough estimate. With enough blood stains present, investigators would eventually establish the point of origin. There are programs that create a virtual environment where investigators can input blood stains and determine the points of origin.
Blood can be considered both a class characteristic as well as an individual characteristic. If one examines the blood type, then blood would be considered a class characteristic since multiple people would have the same blood type. If one examines the DNA of the blood, than it is considered an individual characteristic since DNA itself is an individual characteristic.
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Blood drop size varies on the type of surface it lands on. The diameter of the drop was largest
on the newspaper than the other surfaces. Surfaces like glass created irregular shaped drops. 2. Determining angle of impact by ruler has substantial leeway. It did not have to be a specific
degree, but if it was within five to ten degrees then it was acceptable. 3. While bloodstains may travel in the same direction, it does not mean there is going to be one
point of convergence. There could be several convergence points close to each other. 4. The only way to have a chance to be any of the four blood types is if one's parents are AO and
BO. Their child has an equal chance to be any of the blood types. 5. A blood drop's tail's length is determined by how acute the angle of impact is. At 90 degrees,
the drop is essentially a perfect circle, but as the angle of impact decreases, it starts growing a tail.
WORKS CITED Fisher, Barry A. J. Techniques of Crime Scene Investigation. Boca Raton, FL: CRC, 2004. 207-10. Google Books. Web. 24 Oct. 2010. Freeman, Shanna. ""How Bloodstain Pattern Analysis Works"" Howstuffworks "Science" Web. 25 Oct. 2010. <http://science.howstuffworks.com/bloodstain-pattern-analysis.htm>. Lotter, Karen. "Luminol - Chemiluminescent Blood Detector: Forensic Investigators' Essential Tool for Crime Scene Investigation." Suite101.com: Online Magazine and Writers' Network. 19 Dec. 2007. Web. 25 Oct. 2010. <http://www.suite101.com/content/chemiluminescent-luminola38625>. "Rihanna's Blood-Stained Dress To Be Presented As Evidence In Case Against Chris Brown." ExpoSay. 5 Mar. 2009. Web. 25 Oct. 2010. <http://www.exposay.com/v/28013/rihannasbloodstained-dress-presented-evidence-case-against/>. Schiro, George. "Collection and Preservation of Blood Evidence from Crime Scenes." Crime Scene Investigator Network. Web. 25 Oct. 2010. <http://www.crime-sceneinvestigator.net/blood.html>.