Please enable JavaScript.
Coggle requires JavaScript to display documents.
Scientific Approaches in Bloodstain Analysis - Coggle Diagram
Scientific Approaches in Bloodstain Analysis
Chapter 1
Background of the Study
discrepancies involving a North Carolina, Wake County Crime Lab
an expert in bloodstain pattern analysis presented fraudulent lab findings which indicated Greg Taylor's truck gave a chemical indication for the presence of blood
bloodstain evidence has been under a great deal of scrutiny
judges have exonerated and thrown out numerous wrongful convictions cases based on the results of bloodstain analysis
Purpose and Objectives of the Study
serves to examine the scientific methodology of bloodstain analysis at the crime scene
the projects focuses on:
physical properties of blood
velocities of blood spatter
theory of blood spatter and angle of impact determination
documentation of bloodstain at the crime scene
provide information about investigative protocol that is used when the investigator arrives at the crime scene
Rationale for the Study
the study of bloodstains provides forensic investigators with important information when conducting a criminal investigation
bloodstain analysis is based on principles derived from: biology, chemistry, physics, and mathematics
explore methodological bloodstain analyses that yield reliable and verifiable evidentiary findings
Limitations of the Study
subjective research-based methods and findings
this study only draws from more practical scientific knowledge that encompasses disciplines such as: biology, chemistry, and physics
Research Hypothesis
first hypothesis: calculating the angle of impact of blood droplets yield conclusive findings about origination of blood
second hypothesis: blood mist is usually caused by gunshot injuries
third hypothesis: bloodstain analysis by proxy utilizing photographic documentation reveals causations of bloodstains
Chapter 2
Forensic Serology
forensic serology
serologist perform tests to analyze other bodily fluids found at the crime scene, such as urine or semen
determines the blood type found at the crime scene, while examining antigens and antibodies
the science of analyzing and studying blood evidence found at the crime scene
research from Ronald F. Becker (2009)
"biological evidence can exist in the form of blood and other bodily fluids such as spittle, semen, vaginal secretions, or any other DNA source, such as bone or tissue.."
serologists have long been able to identify the presence of sperm and semen by testing for acid phosphates or by microscopic examination for sperm cells
Biology of Blood
blood is a tissue that is circulated within the body to assist other parts of the body
consists of fluids called plasma and three types of blood cells: red, white, and platelets
classified in four main groups: A, B, AB, and O
the primary function of blood is to supply oxygen to tissues throughout the body, remove waste such as carbon dioxide, urea, and lactic acid, and regulate core body temperature and ph- levels, and transport hormones throughout the body while circulating white blood cells and antigens to repair the body
Viscosity of Blood
considering blood is a fluid therefore is an intrinsic property of viscosity
a measurement of the resistance of a fluid that is impacted by either shear stress or tensile stress
viscosity simply refers to thickness of a fluid, meaning how thick a fluid is
the higher the hematocrit (ratio of hemoglobin to whole blood) values of blood, the higher its viscosity
as fluid becomes more viscous, the more slowly the fluid flows due to specific gravity
Blood Flight Characteristics
when blood travels through the air it forms a tear drop shape due to the surface tension as it leaves the blood source
blood exposed to atmospheric conditions is subjected to various forces, such as specific gravity and force
surface tension will cause the blood drop to pull itself in; both horizontally and vertically
as the blood droplet strikes a horizontal surface at ninety degrees it creates a circular stain
as blood travels dropping downwards on a horizontal surface it becomes elongated and oval shaped stains are created
blood does not travel in a straight line but in what is called a parabolic arc which is subjected to Earth's gravitational pull and air resistance
forces such as gravity or impact will affect the size rather than the shape of the blood droplet
the size or diameter of a blood droplet produced by free-falling blood will increase with distance based on origination of blood source at about seven feet
Chapter 3
Angle of Impact
using basic mathematical and scientific principles, bloodstain pattern analyst can determine the angle of impact, and then provide the source of where the blood originated
by measuring the length and width of the splatter, dividing the width of the splatter by its length, we can determine the impact angle
the angle of impact is the second measurement needed to identify the origination of the blood source
AOI = arcsin(width/length)
in determining the angle of impact in respect to the bloodstain pattern, the area of origin can be calculated
Case Study 1
The Case
January 2000, elderly woman was raped in her home
offenders DNA was left at the scene in which bloodstains were discovered
March 2000, a woman was raped and murdered in her home
DNA evidence also was recovered at that scene and matched DNA in the January 2000 case
March 2005, Raymon McGill was convicted of a robbery that required him to provide a DNA sample for the criminal databank
Scene of the Crime
blood: present in various places in the room; small amounts were present on the walls; large amounts of blood were found in the victim's bedroom and on the floor
blood spatter: result of the bloodstain pattern study at the scene revealed that the intruder left blood at the crime scene; presence of bloodstains in the rooms confirmed that a weapon was used in which a physical struggle took place, between the victim and the intruder
Chapter 4
with close analysis of bloodstains the investigator can determine the following:
type of velocity of the weapon used
number of blows inflicted
position and movements of victim and assailant during the attack
type of injuries
when crime was committed
which wounds were inflicted first
Bloodstain Interpretation
bloodstains can be classified as low velocity, medium velocity, or high velocity impact stains
velocity does not describe the speed of the blood droplet as it take flight in the air
describes the amount of force and energy that is directed upon a specific blood source which creates the stain
low velocity bloodstains are the result of dripping blood on a target surface
medium velocity bloodstains can be associated with objects that produce external forces of greater than 5ft/sec and less than 25ft/sec
blood misting is usually caused by gunshot injuries
in this specific case (high velocity) objects are moving in excess of 100 ft/second
the analyst uses trigometric laws of a right triangle to find the point of origin and actual path of the blood droplets
Chapter 5
Discussions
bloodstain analysis by proxy utilizing photographic documentation reveals causations of bloodstains
investigators must take overview, medium-range, and close-up photographs of each bloodstain using an indication scale
even in adequate photos are taken, bloodstain pattern analyst can determine causation and what type of object was used in crime
UNDER NO CIRCUMSTANCES SHOULD EVIDENCE CONTAINING MOISTURE BE PACKAGED IN PLASTIC OR PAPER CONTAINERS FOR MORE THAN TWO HOURS
each package or container must include the include the following:
the collecting person's initials
the date and time it was collected
a complete description of the evidence and where it was found
the investigating agency's name and file number
protective clothing, gloves, masks and eye protection should be worn throughout the entire crime scene
Conclusion
forensic science is the scientific processing of information found at the crime scene
blood is one of the most common types of physical evidence found at a crime scene
understanding how blood interacts with various surfaces is most important during analysis