Blood and Blood Spatter Serology Blood Spatter Analysis

Blood and Blood Spatter Serology Blood Spatter Analysis Three Main Questions a Forensic Scientist must answer about blood: 1) Is it blood? (Peroxidase test) 2) Is it human? (Precipitin test) 3) What type? (A-B-O typing)

Serology What is serology? Serology is the study of serums, or bodily fluids. Examples: n n Blood Saliva Sweat Etc.

Ludwig Tessnow Case Germany 1901. Ludwig Tessnow was accused of murdering two children. He claimed red stains on his clothes were wood dyes. Paul Uhlenhuth – discovered how to test for blood and to distinguish between human and animal blood. Tessnow’s clothes were tested. The results showed the stains were not dyes, but blood. As a result Ludwig was convicted of murder and executed in 1904.

Blood Typing In 1901 Karl Landsteiner discovered the human blood groups. The difference in blood groups are due to the presence or absence of certain protein molecules called antigens and antibodies. Landsteiner broke the groups into the familiar A, B, AB, and O. Blood Type Antigen Antibody % A A B 42 B B A 10 AB A&B None 4 O None A&B 44 Responsible for clotting

Blood Typing Besides A, B, AB, and O there are over 100 blood factors that can be used to identify a person. Example: RH factor (+ 85%, - 15%) Until the 1990’s scientists used these factors to identify someone. Today we use: DNA

How much blood do we have? o o o You have about 10 pints of blood pumping through your body. This makes up about 8% of your weight Plasma is the liquid portion of blood and it is 55% of the blood volume. Red blood cells (or erythrocytes) transport oxygen from the lungs and carbon dioxide to the lungs for removal. n Antigens on the surface of the RBC give them their blood characteristics. White blood cells (or leukocytes) produce antibodies to disable and/or destroy invaders. Platelets (or thrombocytes) help to clot blood. 55% 45%

Secretors What is a secretor? A secretor is defined as a person who secretes their blood type antigens into body fluids and secretions like the saliva in your mouth, sweat, etc. As a general rule, in the U. S. 80% of the population are classified as secretors.

Blood at the Crime Scene Is it blood? Blood contains peroxidase, which gives off colors when exposed to different chemicals. We use presumptive tests to answer this question. Hemastix – reacts with the hemoglobin in blood. Hemastix will turn from yellow to dark green if blood is present.

Blood at the Crime Scene o Presumptive Tests (continued) n Kastle-Meyer Test o A drop of phenolphthalein reagent is added to the sample, and after a few seconds, a drop of hydrogen peroxide is applied to the swab. If the swab turns pink rapidly, it is said to test presumptive positive for blood.

Blood at the Crime Scene Presumptive Tests (continued) Luminol – reacts with iron present in blood and a chemical reaction that leads to luminescence revealing the location of the blood. Picks up blood even if diluted up to 10, 000 times. False positive results may occur in the presence of radishes and citrus.

Blood at the Crime Scene From what species? Precipitin or Gel Diffusion – Blood from mummies 4, 000 – 5, 000 years old still give positive results! If it’s human blood, whose is it? n n ABO Testing DNA Fingerprinting

Interpreting Blood Spatter o Blood spatter can tell us the following: n n n Direction blood droplet was moving Where the blood droplet came from Type of weapon used in the crime Position of victim, suspects, and objects Sequence of events

Interpreting Blood Spatter How to tell the direction that blood droplet was moving. Here is a picture of some blood spatter which hit a surface. The pointed part of the blood spatter gives you the direction the blood was traveling at the point of impact.

Interpreting Blood Spatter o Working with multiple droplets can tell were the victim was located when the crime was committed. Voids on the patterns indicates shielding by the suspect and other objects

Types of Blood Spatter Passive blood spatter is created by the force of gravity. Height determines diameter of blood spatter. As height increases The diameter of the blood drop increases Irregular spattern indicate higher fall.

Types of Blood Spatter o Projected blood spatter occurs when energy has been transferred to the blood source. n Low, Medium & High Velocity o Falling blood drops (1 -4 mm, ~5 ft/s) o n n Gunshot wounds (<1 mm, ~100 ft/s) High Velocity Arterial Spurting o Cutting of an artery (Large amounts of blood) Expiratory o Blood from mouth or nose Arterial Spurting or gushing

Types of Blood Spatter o Contact or Transfer blood spatter occurs when an object with blood on it comes into contact with other objects. n n Wipe Swipe

Angle of Impact o o The angle of impact is useful in determining where blood spatter originated from. To find the angle of impact: Sin (angle) = Width / Length

As the angle increases Eccentricity decreases (it looks rounder)