Forensic Science Forensic Serology Composition of Blood Blood

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: Antigens proteins on surface of cells (including RBCs) that identify them – Different types of cells have different antigens • Antibodies: Antibodies Y-shaped immune system proteins that recognize and bind to foreign objects to neutralize them – You get vaccines to develop these! • Agglutination: Agglutination clumping of antibodies when they bind to their specific antigen 3

ABO Blood System • • Blood Type Antigens on RBCs A A Antibodies in Blood Serum 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 A B AB O DONATES TO A, AB B, AB AB A, B, AB, O RECEIVES FROM A, O B, 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 O ALLELE COMBINATIONS AA, AO BB, BO AB OO Punnett Square 7

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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: 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 KM result, but… you’re probably not going to find those at a crime scene

Is it blood? • Luminol: Luminol When sprayed on blood, this solution produces a faint blue light – This can work on blood that someone tried to clean up

(Luminol demos)

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 Spatter Analysis • Blood spatterns can be used to recreate a crime scene. It is possible to determine: – The direction the blood was travelling – The angle of impact – The point of origin of the blood • This can help determine the manner of death

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

Blood Spatter Analysis - Speed • Size of blood drops tells us about the speed of the drop upon impact – Small droplets (less than 1 mm; spray) mean high velocity around 100 ft/s • Example: gunshot wound – Medium droplets (1 -4 mm) mean medium veloc 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

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. 20

(stop) Lab: Affect of Height on Size of Blood Drops

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

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 sin 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

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

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

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

• Remember SOH CAH TOA hy opposite height = tan 27° x 5. 75 ft height = 0. 5095 x 5. 75 ft height = ~2. 9 ft above the ground po so height = tanθ x distance te nu tanθ = height/distance to convergence se – Tangent is opposite/adjacent angle adjacent Yay math!

Add this formula to your notes… To find the height of the origin of blood spatter… height = tanθ x distance to convergence 31

Blood Spatter Analysis - Origin DEXTER • You can use string to help you recreate point of origin • There also computer programs to help – “No More Strings”

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

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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 36

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 37

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

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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 Mc. Gunagle http: //www. trutv. com/library/crime/notorious_murders/fa mous/sheppard/index_1. html 40