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"Scientific Approaches in Bloodstain Analysis" by William Y.K.…
"Scientific Approaches in Bloodstain Analysis" by William Y.K. Trumbo
Forensic Science is related to what is found at a scene of a crime
Evidence
Blood and the interactions it has
Chapter 1: Introduction
Mandy Locke article
Wake County Crime Lab
Bloodstain evidence looked at a lot for invalid analysis
Wrongfully convicted individuals (about 40 in Texas)
Bloodstain analysis calculations and error rates
Increase precision
arcsin (w/l) = AOI
Physical properties of blood
Blood spatter velocity
Angle of impact
documentation
Overall, mid-range, and close-up photos
Look at weapon velocity, how many times the victim was hit, location of victim and suspect, injuries, approximate time, and sequence of events
Documentation and collection of blood evidence
Blood pattern analysis can help in reconstruction
Factors that effect bloodstains
It is important to have extensive knowledge in basic blood and bloodstain analysis terminology
High velocity impact pattern - blood mist
Chemistry, biology, physics, and math
Chapter 2: Literature Review
Forensic serology - blood, urine, or semen
Antibodies, antigens, who's blood is it, and who else was ther e
A, B, AB, O blood types (antigens present on surface) and Rh factors
Ronald F. Becker - class and individual characteristics of blood
Other biological evidence
Wet bench serology...blood types an antigens
Acid phosphate for semen and testing if sperm is present
Amylase - saliva
Reconstruction: location, size and shape help and so does distribution of stains
"Taxonomy of stains"
Blood: Connective tissue, made in bone marrow, RBC (erythrocytes), WBC (leukocytes - immune), and platelets, plasma
Leukocytes: neutrophils, monocytes, eosinophils, basophils, and lymphocytes
WBC have nucleus...this is where chromosomes are
DNA in nucleus: nucleotide - A,C,G, and T
viscosity = thickness of material (fluid material) - blood is thicker than water
Newton's Law of viscosity
y=v/h
The more viscose something is the thicker it will be
gravity and air resistance
Tom Bevel said bloodstains are reproducible
Blood in flight
Surface tension makes blood settle in a spherical pattern
surface tension decreases surface area
90-degrees creates a circle stain
Porous vs nonporous surface will change the way blood drops on a surface
Porous surfaces will not have as much splash as a nonporous surface would
Decreasing the angle of impact will increase the elongation shape of the stain
parabolic manner of travel ...y=ax^2+bx+c
Terminal velocity is the max, acceleration of the droplet when it is free-falling
The smaller the drop the smaller the terminal velocity
Tails on bloodstains can indication directionality
Length of the bloodstain increases as angle and distance increases
Point of origin
initial position of bloodstain
3-D representation in space
Chapter 3: Methodology
Angle of Impact: arcsin (w/l)
Origin
Right angle trig.
Point of convergence
Tan(AOI)*d
Bloodstain will be more circular if dropped at a higher height
Case Study
Bloodstain from a January and March 2000 and a case in 2004 all has DNA that was consistent with DNA that was found at each scene ---- Rayon McGill
Crime Scene
To reconstruct the bloodstains that were analyzed
Lab can determine who may have left the blood
Stringing Method
Chapter 4 : Results
Bloodstains analysis through science
Velocity, numbers of hits, location of victim and suspect, injury, what type of crime was committed, and wound sequence
Bloodstain Interpretation
Low, medium, and high velocity
Energy and force
Directionality of the bloodstain
Stringing Method
AOI
Right angle trig.
Size of droplet
Cast-off patterns
Low and medium velocity hits may create this type of pattern
Mist
High velocity - example: gunshot
Direct blow from bullet - larger wound
Shock wave from the bullet - tissue damage increases
Different injuries may leave distinct bloodstain patterns
Example: arterial spurts
Chapter 5: Discussions, Conclusions, and Recommendations
Photos of the crime scene are helpful and must show the crime scene as it was found
Overall, mid-range, and close-up photos
collection of evidence in the correct manner is vital in reducing degradation
Chain of Custody