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Scientific Approaches in Bloodstain Analysis (Crime Scene Investigation) …
Scientific Approaches in Bloodstain Analysis
(Crime Scene Investigation)
By: William Y. K. Trumbo
Forensic Science
Collecting evidence
Evidence is used in court
Bloodstains are a common piece of evidence and help determine:
Point-of-origin
Area-of-origin
Angle of impact (AOI)
Point-of-convergence
What direction in which the bloodstain was traveling
Has not always been accepted by court system
CSI have to know what evidence is essential to collect in order to solve a crime
Evidence has to be concealed, and chain of custody must be followed in order to keep integrity of evidence intact
Photographs should be taken
Close-up
Mid-range
Overview
Evidence should be packaged in appropriate containers
Example: wet evidence is put in a plastic bag and transported to lab where it can be properly dried in a non-contaminating area
Bloodstains as Evidence
Includes:
Physical properties
Newton's Laws
Force= mass * acceleration
Laws of gravity
Viscosity
Resistance by sheer or tensile stress
Fluids thickness
Surface tension
Air resistance
Blood flight characteristics
Determines shape of blood when it impacts a surface
Chemical properties
Slightly basic
Mathematical properties
AOI
Determined by length and width of bloodstain
Used to find origin
Point of origin
Uses 3 dimensional space
Trigonometry; right triangle
Point of convergence
Parameter of bloodstain and angles
Biological properties
Forensic serology
Determines:
Antigens and antibodies present in the blood
Assists in identifying who the blood belongs to
Serologists can testify in court
Acid phosphate tests or microscopic examinations are used to see if sperm is present
Can identify the presence of saliva, urine, vaginal fluids and fecal matter
Has both class and individual characteristics
Blood cells
Produced in the bone marrow
Contains red blood cells, white blood cells and plasma
Plasma is 55% of blood
Red blood cells carry oxygen through the body
White blood cells contain leukocytes
Blood has types A, B, AB, and O
RH factor can make blood either negative or positive
Piecing together information
Can lead to a accurate analysis of the events that happened at a crime scene
Can identify number of times a victim was struck, weapon used, series of strikes, and movement of individuals
Velocity
Based on force
Low velocity
Low force is acted on by gravity and is in free fall
Often creates a 90-degree angle
Medium velocity
Struggle
Violent movement (ex: stabbing)
Cast-off
Arterial spurt
High velocity
Gunshot
Analysis of Bloodstains
Can help with determining:
Identifying the type of weapon used
Number of times the victim was struck
Positions of both the victim and attacker
What kinds of injuries were sustained
The time at which the crime was commited
The sequencing of wounds
Hypotheses
Hypothesis 2: Gunshot wounds on a person moving more that 100ft/sec will result in more of a mist pattern
Hypothesis 3: Bloodstain analysis can determine the cause and weapon used in a crime if there is proper documentation and photos taken of the bloodstains.
Hypothesis 1: By mathematically determining the AOI, the injuries, blunt force trauma and number of times a person was hit with an object can be analyzed