Forensic Science Parts of blood Red blood cells Carry Oxygen Contain the antigens Most abundant cells in body White blood cells Part of the immune system Plasma Yellowish liquid containing electrolytes Contains the antibodies Platelets Coagulation - clotting Blood Transfusions Blood transfusion attempts often ended in failure due to clotting 1901 Karl Landsteiner A-B-O blood typing Based on blood factors attached to red blood cells Since then more than 100 different factors have been identified Antigens vs. Antibodies The type of Antigens on your red blood cells determines your blood type A, B, AB, O Also called agglutinogen Antibodies (agglutinin) Contained in blood serum Anti-A, Anti-B, Anti-D contained in (anti-serum) Antibodies react with their specific antigen and create clumping called agglutination ABO Blood System Rh Factor Blood Factor D Present = +, non present = - A+ A- B+ B- AB+ AB- O+ O- Rhesus monkeys How blood can be used Blood samples Can be analyzed to determine BLOOD TYPE and DNA, which can be matched to possible suspects. Blood droplets Can be analyzed to give clues to the location of a WOUND, movement of a VICTIM, and type of INJURY. Blood spatter Can be analyzed to determine PATTERNS that give investigators clues to how a crime might have happened. Blood Type Distribution Blood Typing 14. Use the results shown to determine the blood type for each sample. - = No Clumps + = Clump A B Rh Blood Type: ___ To determine a persons blood type, we add three different serums to blood samples and see if clumps form. Clumps = Positive (+) No Clumps = Negative (-) What would the blood type be for this sample? Collecting Blood Samples Collection for Analysis Q-tip Distilled water Presumptive blood tests Kastle-Meyer Based on hemoglobin present in blood Mixture of blood, indicator, & hydrogen peroxide produces pink color Can produce false-positives with some types of vegetables. Hemastix Strips Designed to find blood in urine Available at drug store Is it blood? Verification of human blood vs. animal blood Animal & Human serums with antibodies Microscopic observation Precipitin testblood is injected into a rabbit; antibodies are formed; the rabbits blood is extracted as an antiserum; the antiserum is placed on sample blood. The sample will react with human proteins if human blood is present. This test is very sensitive and requires only a small amount of blood. Animal Blood Larger nucleic red blood cells Frog Blood Human Blood Red blood cells are most numerous; 5 to 6 million per mm 3 White blood cells are larger and less numerous; 5 to 10,000 per mm 3 Platelets are tiny, cellular fragments; 350 to 500,00 per mm 3 Luminol Reaction with blood (1ppm) produces light Luminol solution is sprayed and room is darkened Allows ability to survey large area at a time May show traces of blood that are invisible under normal conditions Reacts also with: Bleach, Cu, Fe, Co, plaster Blood Spatter Evidence Important Factors: Surface texture Generally, harder/less porous surfaces result in less spatter Shape determines direction Pointed end of blood always faces its direction of travel Distortion determines angle Elongation can lead to angle of impact Lines create convergence Drawing lines can determine where the blood originated Drop Height & Diameter Input values in excel spreadsheet Higher drop heights = higher velocity blood spatter Direction, Shape & Angle Pointed end determines direction Demonstration on board Shape determines angle Accepted variance = 5-7 0 Point and area of convergence The point of convergence is the intersection of two bloodstain paths, where the stains come from opposite sides of the impact pattern Point and area of convergence The area of convergence is the box formed by the intersection of several stains from opposite sides of the impact pattern 3-Dimensional Combine convergence & angle of impact 3 methods of accomplishing this Method #1 Area of Origin (AOO) via Graphing Measure distance between the back of the stain to area of convergence (AOC) Determine Angle of Impact (AOI) using sin -1 Create a graph Height vs. distance (cm) Scales must be the same Method #1 Graphing Distance = 24cm AOI = 41 degrees Distance of stain to AOC Height above bloodstain Do this for minimum 3 bloodstains