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Forensic Science: Blood Analysis and Blood Spatter at a Crime Scene

Forensic Science: Blood Analysis and Blood Spatter at a Crime Scene. By: Monica Ye & Lilliana Mendoza Mentor: Dr. John Molina Bronx Community College. Nature of Blood. Blood is a mixture of cells, enzymes, proteins, and inorganic substances.

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Forensic Science: Blood Analysis and Blood Spatter at a Crime Scene

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  1. Forensic Science:Blood Analysis and Blood Spatter at a Crime Scene By: Monica Ye & Lilliana Mendoza Mentor: Dr. John Molina Bronx Community College

  2. Nature of Blood • 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 other portion of blood is the cellular phase. This contains red blood cells, white blood cells, and platelets. • Antigens are proteins located on the surface of red blood cells and are responsible for blood type characteristics. • The most important types of antigens are A-B-O. • Type A has A antigens in one’s red blood cells. Type B has B antigens. Type AB has AB antigens, and type O has neither A nor B antigens.

  3. For every antigen there is a specific antibody that will react with the antigen to form clumps known as agglutination. For example, if anti-B is added to red blood cells carrying B antigen; there will be a reaction.

  4. Importance of blood at a crime scene: • The blood that is found a crime scene contain Deoxyribonucleic Acid (DNA). • DNA is found in the nucleus of cells which contains the genetic material of living organisms. • DNA is used to identify the victim(s) and the killer involved. • Blood can also be used to determine the sequence of how a crime occurred. • The blood that is found can be used to determine what weapon (if any) was used in the crime. • Blood can also help identify the origin of the blood.

  5. Identifying Blood • When blood is found at a crime scene, it is possible that the substance may not be blood at all. • A preliminary or screening test procedure is used to determine if the substance is blood; this preliminary or screening test procedure is called Presumptive Testing. • Presumptive Testing is based on the reactivity of hemoglobin, a protein found in red blood cells used to carry oxygen throughout body. Two different chemicals are used in this test: Phenolphthalein and O-toluidine.

  6. How are the chemicals used? • - A sample of the blood is taken on a Q-tip and a small amount of the chemical is dropped on to the sample. - If the substance is blood, when Phenolphthalein is used; the sample will turn pink. If O-toluidine is used; a green-blue color will appear. When these colors appear, it doesn’t necessarily mean that it is blood. The blood sample needs to undergo another procedure that confirm the presence of blood. • Both Phenolphthalein and O-toluidine reacts to the Hemoglobin, which is an oxygen- carrying protein in the red blood cells.

  7. The Takayama Test • A sample of the blood is placed on a slide and examined under a microscope. • If the substance is bloodcrystal-like shapes will form. • If the substance is not bloodno crystals will form.

  8. PCR Analysis • After we confirm that the substance found is blood at the crime scene; PCR analysis is used. PCR stands for ‘polymerase chain reaction’. This is a technique that is used to create millions of copies of DNA just using a single sample of DNA. • This technique is used by forensic scientists to perform DNA analysis on really small samples; such as skin cells. • So from the blood substance, DNA is extracted and then analyzed using this procedure. • Other tests may include: STR (Short Tandem Repeat testing), RFLP (Restriction Fragment Length Polymorphism).

  9. Blood Spatter • 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 blows and gunshots the victim received -sequence of events

  10. Categories of Blood Stains • There are three basic types of blood stains: - 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.

  11. Direction of Blood Stain -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.

  12. Angle of Impact -At a 90 degree angle, the blood drop is circular and there won’t be any short or long axes. -Below 75 degrees, the spines become more prominent on the side of the spatter opposite the angle of impact. -At highly acute angles; usually below 40 degrees, the blood drop begins to form tails and a second spatter coming from the first one. -The angle of impact can be determined by taking the inverse sine of the width over the length of the blood stain. Example: SIN  = Width (a) 1.5cm Length (c) 3.0cm Width (a) 1.5cm = 0.5 = SIN  Length (c) 3.0cm   = 30O

  13. References • Slemko, J. "BLOODSTAIN PATTERN ANALYSIS TUTORIAL." Homepage. Web. 28 July 2009. <http://www.bloodspatter.com/BPATutorial.htm>. • Forensic Science Service Ltd. "Forensic Science Service - Blood Pattern Analysis." Forensic Science Service - Home Page. Web. 28 July 2009. <http://www.forensic.gov.uk/html/services/analytical-solutions/blood/>. • Mindrelief.net. "Blood in the Crime Scene." Custom essay, term paper, research paper writing service. Web. 30 July 2009. <http://www.mindrelief.net/blood.html>. • Old Spring Harbor Laboratory. "Cutting, Pasting, & Copying DNA & the Recombinant DNA Controversy." DNA Interactive: Discovering the DNA Structure and beyond. Web. 03 Aug. 2009. • "RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>. • "RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>. • PBS. "A Science Odyssey: DNA Workshop: Replication." PBS. Web. 03 Aug. 2009. <http://www.pbs.org/wgbh/aso/tryit/dna/replication.html>. • "RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>. • Think Quest. "Forensic Science | Blood Analysis." Oracle ThinkQuest Library. Web. 05 Aug. 2009. <http://library.thinkquest.org/04oct/00206/lo_pti_blood_analysis.htm>. • http://www.bloodspatter.com/terminology.pdf • http://www.nfstc.org/links/animations/images/blood%20spatters.swf

  14. Acknowledgements • Dr. John Molina • Dr. Sat Bhattacharya • Bronx Community College • National Science Foundation • Harlem Children Society • Harlem Children Society Staff • Audience

  15. Thank You!

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