Forensic Science Forensic Serology
Composition of Blood Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances Main Components: Erythrocytes = red blood cells (RBCs) Leukocytes = white blood cells (WBCs) Platelets = clotting factors Plasma = the liquid part 2
Antigens and Antibodies Antigens: proteins on surface of cells (including RBCs) that identify them Different types of cells have different antigens Antibodies: Y-shaped immune system proteins that recognize and bind to foreign objects to neutralize them You get vaccines to develop these! Agglutination: clumping of antibodies when they bind to their specific antigen 3
ABO Blood System Blood Type Antigens on RBCs Antibodies in Blood Serum A A anti-b B B anti-a AB A and B none O none anti-a and anti-b Anti-A antibodies will agglutinate (clump) in Type A blood Anti-B antibodies will agglutinate in Type B blood Type AB blood will agglutinate in anti-a or anti-b serum Type O blood will not cause agglutination 4
Blood Donors and Recipients BLOOD TYPE DONATES TO RECEIVES FROM A A, AB A, O B B, AB B, O AB AB A, B, AB, O O A, B, AB, O O Type AB blood is the universal recipient because it can take any of the 4 types and not agglutinate Type O (most common) is the universal donor it does not have any antigens to cause agglutination 5
Rh Factor Rh (Rhesus) factor is another important blood antigen This is the positive (+) and negative (-) of blood types Rh- means you don t have the antigen Rh factor affects blood donation compatibility Rh+ blood types can accept either Rh+ or Rh- Rh- can only accept Rh- blood or it will agglutinate 6
Genetics of Blood Blood types are determined by looking at 2 inherited genes (one from each parent) There are 3 common alleles for blood types: A, B, and O, with 6 possible combinations BLOOD TYPE A B AB ALLELE COMBINATIONS AA, AO BB, BO AB Punnett Square O OO 7
Biological Properties of Blood Blood delivers nutrients and oxygen to the cells and transports waste products away from cells. Red blood cells carry oxygen and carbon dioxide.
Biological Properties of Blood White blood cells fight off infection and reject foreign tissue.
Biological Properties of Blood Platelets assist in clotting.
Forensic Science Blood Stain Analysis
Testing for Blood When they find a red stain, investigators must ask themselves 3 questions: 1. Is it blood? 2. Is it human blood? 3. Whose blood is it?
Is it blood? Presumptive tests (color tests) indicate the presence of blood Kastle-Meyer: this solution of phenolphthalein turns bright pink when it encounters the blood protein hemoglobin Some vegetable matter like potatoes and horseradish can give a positive K-M result, but you re probably not going to find those at a crime scene
Is it blood? Luminol: When sprayed on blood, this solution produces a faint blue light This can work on blood that someone tried to clean up
Is it human or animal blood? Precipitin Test Serum made in rabbit contains antibodies against human blood Crime scene blood is layered on top of the anti-human serum in a test tube If the sample is positive for human blood, a cloudy precipitate will form where the 2 layers meet
Whose blood is it? A DNA analysis would have to be performed to find out exactly who the blood belongs to But ABO blood typing can narrow down a pool of suspects.
Blood Spatter Analysis Passive Dripping Transfer Impact Spatter: Occurs when an object impacts a source of blood
Blood Stain Evidence Bloodstain patterns can help investigators reconstruct events in a crime scene. Analysis of the blood stain can tell whether it is animal or human. Projected blood stains are called blood spatter.
Blood Spatter Blood spatter analysis can approximate: distance from the source of the blood to the pattern direction from which the blood impacted speed the droplet was traveling location of the point of origin movement of a bleeding individual throughout the scene These approximations may agree or disagree with statements made by witnesses, victims, or suspects. This can help determine the manner of death
Physical Properties of Blood Unlike water, blood is a suspension of solids and gases in a liquid. Blood behaves differently than water when it is moving. The viscosity of blood lowers as its shear rate increases (pumps easier at high flow rates).
Physical Properties of Blood The surface tension of blood is slightly less than water. Blood forms a spherical projectile, not a teardrop. A large amount of blood from a small wound means that the victim survived for a fair length of time. Blood normally clots in 3-15 minutes.
Physical Properties of Blood Fluid flow is driven by a pressure difference. Blood pressure drops with excessive blood loss and the bleeding rate slows due to this lower pressure difference. Upon death blood pressure falls to zero and bleeding stops.
Blood Spatter Analysis - Surface When examining blood spatter, is it important to consider the surface Hard and nonporous surfaces like glass and tile generally result in round drops with less spatter Rough surfaces like carpeting, wood, or fabric usually result in irregularly shaped stains with serrated edges and possibly satellite spatter Satellite spatter are the tiny droplets that break away from the main drop
Surface Tension Surface tension acts to reduce surface area. It resists penetration and separation. The smallest surface area to volume ratio is a sphere, which is why blood droplets fall in a spherical rather than teardrop shape. This sphere of blood does not break up until impact with a solid surface.
Drop Sizes The standard drop size is about 0.05 ml. Rapid bleeding gives a slightly larger drop. Shaking movement casts off smaller drops. Gunshot wounds produce high velocity spatter that results in a spray of very tiny drops.
Blood Spatter Analysis - Speed Small droplets (less than 1 mm; spray) mean high velocity around 100 ft/s Example: gunshot wound Medium droplets (1-4 mm) mean medium velocity around 25 ft/s Example: stabbing Large droplets (4-6 mm) mean low velocity around 5 ft/s Example: blunt object impact such as a hammer to the head
Free Falling Blood Droplets Blood droplet size affects both the terminal velocity and the distance that the droplet will fall before reaching terminal velocity. Droplet A B C D Volume (µl) 0.06 0.12 0.50 50 Diameter (mm) 1.10 1.32 2.12 4.60 Terminal Velocity (m/s) 2.2 3.3 4.6 7.5 Distance (m) 0.6 0.9 2.5 5
Free Falling Blood Droplets A smooth surface will cause the spatter to spread out smoothly. An irregular surface will create a broken edge and more small spatter.
Wave Cast-Off When a droplet bounces off a surface the tails of the parent and wave cast-off will point toward each other.
Blood Spatter Analysis - Height How far from the ground a blood drop originated is reflected in the size of the blood drop. A drop from farther up will spread out more upon impact. 30
Blood Spatter Analysis - Direction Momentum tends to keep blood moving the direction it was traveling In an elongated blood drop, the tail points in the direction of the blood s movement Satellite droplets appear in front of the moving droplet of blood direction of movement
Determining Directionality The impact angle can be determined by measuring the degree of elliptical distortion. At right angles the blood drop is circular.
Blood Spatter Analysis - Angle angle = arcsin (width/length) The angle of impact can be found mathematically Divide the width (shorter side) of the blood drop by the length (longest part) Then take the inverse sin, also called arcsin or sin -1 of that number to get the angle.
Blood Spatter Analysis - Angle The smaller the angle (meaning the source was closer to the floor) the longer and more stretched the blood drop looks
Angle of Impact The bottom of the spatter stain will be more dense than the top of the stain.
Trigonometry and Angle of Impact To determine the angle of impact: Measure the width and length of the blood spatter. Length must be longer than width. Divide width by length. Take the arcsine of your result. This formula will not produce accurate results at extreme angles ( less than 10 or greater than 60 ). sinθ = w l θ = arcsine w l
Blood Spatter Analysis - Convergence You can figure out where blood came from by drawing lines through the long axis of the droplet. Remember the tail (and satellites) indicate the direction blood was moving, so the origin is the opposite direction. Where lines meet is called the area of convergence.
area of convergence
Area of Convergence (2d area) To determine the area of convergence, investigators calculate the direction and angle of many blood stains. For each blood stain analyzed, they place a string at the stain which is parallel to the angle of the blood droplet.
After many strings have been placed, a general area of convergence will appear where the strings overlap. Area of Convergence (2d area) This can also be done on a computer with image analysis software.
Blood Spatter Analysis - Origin DEXTER You can use string to help you recreate point of origin There are also computer programs to help No More Strings
Blood Spatter Analysis Origin Lines of convergence give you a direction that blood came from, but not height. You can use the angle of impact and trigonometry to determine how far up the blood came from
Add this formula to your notes To find the height of the origin of blood spatter height = tanθ x distance to convergence 44
opposite Remember SOH CAH TOA Tangent is opposite/adjacent tanθ = height/distance to convergence so height = tanθ x distance height = tan27 x 5.75 ft height = 0.5095 x 5.75 ft height = ~2.9 ft above the ground angle adjacent Yay math!
Blood Spatter Analysis - Origin Use angle of impact and convergence lines to make an imaginary right triangle You know the angle of impact, you know the adjacent side length Solve for height using the Law of Tangents
The procedure for generating the point of origin is just like the area of convergence, except the angle of impact for each stain is calculated. Point of Origin (3d volume) This is a method of adding a third dimension to the 2d area of convergence calculation. 2d Solution no angular data
The procedure for generating the point of origin is just like the area of convergence, except the angle of impact for each stain is calculated. Point of Origin (3d volume) This is a method of adding a third dimension to the 2d area of convergence calculation. 3d Solution with angular data
Point of Origin (3d volume) The term point of origin is really a misnomer, as the 3d intersection of the strings creates a 3d volume rather than a single point. This can also be done with a computer by taking careful measurements at the scene for each blood droplet s dimensions, location, and direction.
Limitations of our Model Projectiles launched at an angle do not follow a straight line. In our previous example of calculating the point of origin, it would be lower than calculated because the blood would follow an arc rather than a line. This simplified model doesn t account for gravity.
Limitations of our Model At high velocities (gun shots) the linear model of projectile motion is fairly accurate. The model is better suited to disproving testimony than to accurately re-constructing the events at a crime scene. In a real crime scene, the investigator usually uses lasers instead of string to allow others access to the crime scene.
Blood Analysis Wrap Up Ask: Is it blood? Is it human blood? Whose blood is it? Figure out: Speed of impact Angle of impact Area of convergence Point of origin CLASS CHARACTERISTICS: species blood type Rh factor diseases? INDIVIDUAL CHARACTERISTICS DNA profile
Forensic Serology: Other Body Fluids
Other Body Fluids: Saliva Consists of water, mucin for lubrication, amylase enzyme for digestion, buccal (cheek) cells that could provide DNA Saliva is often associated with sexual assaults and bite mark evidence Presumptive tests for saliva check for the amylase enzyme 54
Other Body Fluids: Semen Consists of water, spermatozoa, enzymes, salts Semen is often evidence in sexual assault cases Presumptive tests for semen include Black light fluorescence Chemical test for acid phosphatase (enzyme from prostate), turns purple when present Confirmatory tests include microscopic examination for presence of sperm DNA analysis can individualize the sample 55
Other Body Fluids: Urine Urine is composed mostly of water, and also includes urea (nitrogenous compound) and salts. Urine is most often used for the detection of drugs in the body EMIT (Enzyme-Multiplied Immunoassay Technique) test reveals the presence of specific drugs through antibody binding
Resources 0135158494, Saferstein, Richard. Forensic Science: An Introduction. New Jersey: Pearson Prentice Hall, 2011. 0536522820, Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 8 th ed. Upper Saddle River, NJ; Pearson Prentice Hall, 2004. Sam Sheppard by Fred McGunagle http://www.trutv.com/library/crime/notorious_murders/fam ous/sheppard/index_1.html 57