CHAPTER 8 PHYSICAL EVIDENCE: BLOOD

Size: px

Start display at page:

Download "CHAPTER 8 PHYSICAL EVIDENCE: BLOOD"

Ella Simmons
5 years ago
Views:

1 CHAPTER 8 PHYSICAL EVIDENCE: BLOOD

2 Is blood class evidence or individual evidence? What is the function of blood? What information can be determined from a sample of blood?

3 Plasma Mainly water, also proteins, hormones, antibodies, & nutrients Red blood cells (erythrocytes) Carry O 2 and CO 2 Hemoglobin=protein that contains iron binds to O 2 & makes blood red

4 White blood cells (leudocytes) Fight bacteria, viruses, etc Only blood cell with a nucleus Source of DNA Platelets Help with blood clotting Help repair damaged blood vessels

5 Body can discriminate between self and non-self White blood cells recognize foreign invaders Concentrate in location of invasion Engulf and digest intruder Secrete antibodies proteins that assist in immune response

6 1982 Dr. Alec Jeffreys produced first DNA profile

7 Less expensive than DNA profiling Class evidence Can link or exclude a suspect Does not prove guilt Karl Landsteiner developed system for classifying blood types in 1901

8 Blood type is based on the presence or absence of glycoproteins called antigens Proteins (with sugars attached) found in cell membrane of red blood cells Two types of antigens are A, B

9 Discovered in 1940 Alexander Weiner worked with Rhesus monkeys Rh + = Blood has Rh factor Rh = Blood does not have Rh factor

10 Type A (42%) A protein Anti-B antibody Type B (12%) B protein Anti-A antibody

11 Type AB (3%) Both A & B proteins No antibodies Type O (43%) No A or B proteins Anti-A and Anti-B antibodies

13 Proteins secreted by B-lymphocytes (white blood cells) Binds to specific antigens Fits like a puzzle piece Recognizes foreign invader and attaches to it Signals white blood cell to destroy foreign invader

14 If wrong blood type is given, antibodies attack RBC Causes agglutination which is clumping of RBC More than 300 blood group proteins Blood must always be typed and cross checked before transfusions

15 Used to identify and match blood samples 3 separate tests are done Mix blood with antibodies that bind to each protein (A, B, or Rh factor) Agglutination = protein is present Example Agglutination with protein B and Rh factor = B+

18 Blood Type? Blood Type? B- A+

19 To determine probability of two separate events, you multiply their individual probabilities See pg 201 for US population percentages What percentage would have A+ blood? 42% x 85% =.42x.85=.357 = 35.7% What percentage has Type O-, MN? The more blood type proteins you test for, the more you narrow down the suspect pool

20 A group of bloodstains created when a wound is inflicted 1939 First analysis of blood spatter Blood spatter patterns can give information about Origin of the blood Direction of blood Angle of impact Cause of injury

21 As blood leaves the body it falls with gravity Cohesion Blood components stick together as blood falls Remains round when it lands If a drop falls on a flat surface, it will have a curved surface.

22 Natural cohesiveness of blood 22 Forensic Science: Fundamentals & Investigations, Chapter 8

Satellite droplets When blood falls from a height, or at a high velocity, It overcomes its natural cohesiveness, and separates from the main droplet

23 Satellite droplets When blood falls from a height, or at a high velocity, It overcomes its natural cohesiveness, and separates from the main droplet Spiking patterns Form around the droplet edges when blood falls onto a less-than-smooth surface 23 Forensic Science: Fundamentals & Investigations, Chapter 8

24 Smoother surface = smoother sphere of blood Hard, smooth, non-porous surface Example: glass, tile little or no distortion around edges

25 Rough or porous surface Example: concrete, carpet Greater distortion and satellites around the edges

26 Passive Fall Blood falls as a result of gravity Falls at 90-degree angle to floor Circular drops Secondary satellites if surface is textured Examples: Blood dripping from a wound or weapon

27 Arterial gushes or spurts caused by pumping action of heart through damaged artery such as carotid artery in neck Found on walls or ceiling

28 Splashes exclamation point pattern that can tell the position of the victim and direction of blood

29 Smears or transfer blood When a bloody person comes into contact with another surface

30 Trails Trail of blood drops or spurts

31 Pools of blood forms around victim who is bleeding heavily in one spot

32 Round droplets formed by 90-degree drips Droplets with tails or satellite droplets identify direction of origin Void (empty space) could help determine presence of a person or object moved after the attack

wall) Point of impact appears darker and wider Momentum causes

33 Cohesion force of attraction between two similar substances Adhesion attraction between two different substances (blood and wall) Point of impact appears darker and wider Momentum causes tail to form in direction of movement Satellites will appear in front of droplet

34 Direction of Blood

35 Draw a line through the long axis of a group of blood stains to determine where they would intersect 2-D model

36 Use of 2 or more spatter patterns Determine angle of impact 3-D model

37 Cast-off stains Blood thrown off a blood covered object Usually occurs with repeated blows

38 Caused by a strong, explosive force Example: gunshot, sneezing Creates a misting of blood Drops less than 1mm

39 Drops 1-4 mm Beating or stabbing

40 Drops greater than 4mm Blunt object impact Bleeding after initial injury Walking around after being stabbed or punched

45 If stain is found Is it blood? Is it human? Blood type DNA

46 Luminol Used to see blood that may have been cleaned Luminol will react with hydrogen peroxide Iron in hemoglobin will speed up reaction Causes mixture to glow for 30 seconds Is very sensitive so can pick up small amounts of blood

49 Use a presumptive blood test to determine if evidence is blood Kastle Meyer Test Uses hydrogen peroxide and Phenolphthalein to react to the hemoglobin in blood If sample turns pink then positive for blood Leukomalachite green Turns green in the presence of blood

50 ELISA test Enzyme linked immunosorbent assay Antibody-protein reaction Human blood is injected into a rabbit Rabbit produces antibodies against human blood Antibodies are tested against blood sample If a reaction occurs then the sample is human

51 Interpret the findings See if the blood type matches a suspect If it doesn t, excludes the suspect If it does, decide if DNA profiling is needed

Blood and Blood Spatter Chapter 11

Blood and Blood Spatter Chapter 11 1 BLOOD OBJECTIVES You will understand: That an antibody and an antigen of different types will agglutinate, or clump, when mixed together. That the significance of the