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Forensic Science - 09 Blood and blood splatter


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A closer look at how blood and blood splatter is analysed in a forensic science investigation for Year 9 students at Saint Ignatius College Geelong

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Forensic Science - 09 Blood and blood splatter

  1. 1. DRYSDALE CSI Blood and blood splatter. Ian Anderson Saint Ignatius College Geelong
  2. 2. WHAT IS BLOOD?  Blood left at a crime scene can be analysed in several ways. Blood group/type can provide class evidence.  DNA profiling can determine whether blood left at a crime scene belongs matches the blood of a suspect (or victim).  Blood splatter can be used to help recreate a crime scene. 
  3. 3. WHAT IS BLOOD? Average adult has about 5-6L of blood in their body.  Makes up approximately 9% of our body weight. 
  4. 4. WHAT IS BLOOD?  Blood is composed of  Red blood cells (erythrocytes).   Carry oxygen to cells and carbon dioxide away from cells. White blood cells (leucocytes). Several different types.  Involved in defence and immunity  fighting pathogens (disease causing organisms)   Platelets.   Involved in blood clotting. Plasma.  90% water and remainder made up of dissolved proteins, hormones, sugars, amino acids, vitamins, minerals, urea, antibodies, etc.
  5. 5. WHAT IS BLOOD?  Blood has several important functions, including      Carries oxygen to cells. Carries waste (including carbon dioxide, urea & lactic acid) away from cells. Carries disease fighting cells. Involved in blood clotting. Involved in homeostasis. Regulation of body pH.  Regulation of core body temperature. 
  6. 6. BLOOD GROUPS. Blood from one person does not always freely mix with blood from another person. Instead, clumping might occur, which can result in death.  In 1901 Karl Landsteiner found that this response was due to the presence or absence of antigens (proteins on the surface of red blood cells), and is now used to classify a person’s blood type (ABO system).  A = only has antigen A.  B = only has antigen B.  AB = has both antigens A and B.  O = has neither antigens A or B. 
  7. 7. BLOOD GROUPS.  These blood types contain antibodies that react against the antigens. Blood group Antibody in plasma A A antigen anti-B B B antigen anti-A AB A & B antigens no antibodies O  Red blood cells contain no antigens anti-A & anti-B Every person belongs to one of these four blood groups for their whole life.
  8. 8. BLOOD GROUPS.  These blood types contain antibodies that react against the antigens. Blood Group Population A B AB O Aborigines 0 0 34 Australian (nonaboriginal) 39 11 4 46 UK/USA 41 10 4 45 Polynesian 52 0 0 48 Peruvian Indian  66 0 0 0 100 Your blood type is not necessarily unique to you, but is associated with a group of people.  Therefore blood type is regarded as class evidence.
  9. 9. BLOOD GROUPS.  Other blood grouping factors are also now used, incl.  Rh factor.   MN proteins.   ~82% of Australians Rh+ and 18% are Rh-. ~30% of people MM, 22%NN, 48% MN. Combining these other blood grouping factors, somebody can now be placed into one of 288 different blood types.
  10. 10. DNA PROFILING. DNA collected from white blood cells can be used for DNA profiling (also called DNA fingerprinting).  DNA profiling allows a blood sample to be identified with a single person. 
  11. 11. BLOOD SPLATTER. When a wound is inflicted and blood leaves the body, a blood splatter pattern may be created. This pattern can then be used to help reconstruct the series of events surround the shooting, stabbing or beating.  The characteristics of blood drops on surfaces can  Show how the blood was deposited  At what rate the blood was moving  The location of the origin or source of blood  The direction in which the blood was moving when it struck the surface. 