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Chapter 7.2: Bloodstain Pattern Analysis - Coggle Diagram
Chapter 7.2: Bloodstain Pattern Analysis
Introduction
NARS Report
understanding how a particular bloodstain pattern occurred can be critical to physical evidence
helps investigators understand the events of the crime
many sources of variability arise with the production of bloodstain patterns
interpreting and integrating bloodstain patterns into a reconstruction requires, at a minimum:
an appropriate scientific education
knowledge of the terminology employed (e.g., angle of impact, arterial spurting, back spatter, castoff pattern)
an understanding of the limitations of the measurement tools used to make bloodstain pattern measurements (e.g., calculators, software, lasers, protractors)
an understanding of applied mathematics and the use of significant figures
an understanding of the physics of fluid matter
and understanding of pathology of wounds
an understanding of the general patterns blood makes after leaving the human body
Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council (2017)
must be stressed the BPA requires practical study
the crime scene investigator is to take some blood and experiment to try and recreate the stains for accuracy
based on the appearance, size, and location of the bloodstains, BPA can answer many questions about what happened at the crime scene and, sometimes, about what did not happen
human male typically has 5-6 L of blood; human female of the same weight will have 4-5 L
8 bottles of red wine vs. 6 bottles of red wine
freeze the scene; recognize, recover, and record physical evidence; utilize photography, videotaping, sketching, and note-taking
it is the responsibility of the investigator in charge to ensure that all investigators use PPE that includes at minimum:
eye protection, a face mask, a hooded Tyvek suit, rubber gloves, and bootees
Directionality
the direction that bloodstains were traveling when they struct the target
it has been shown by high-speed photography that blood droplets in flight are in the form of spheres
the motion in the 45-degrees example gives rise to a "tail," which when inspected can tell which direction the bloodstain was traveling when it high the target
Droplet Size and Force
the greater the force involved in their production, the smaller the size of the pre-dominant blood droplet
high-velocity spatter
gunshot, with the high energies involved in production, produces blood droplets that are 1 mm and smaller in diameter
medium-velocity spatter
caused by a medium force event (such as a stabbing or beating), give rise to stains that are from 1 to 4 mm in diameter
low-velocity spatter
caused by a low-force event such as blood drops from a nose bleed, generates stains that are large, from 4 mm and up
the term "velocity" refers to the mechanism that created the blood spatter and not necessarily the speed at which the blood hits the surface it is deposited on
Grouping Bloodstains
bloodstains can be grouped according to location, size, and shape
it is likely that groups of bloodstains with similar shape, size, and location are generated by the same event
Types of Bloodstains
passive stains
mostly produced by the force of gravity and include drips, splashes, flows, and pools
impact spatter stains
result of an impact with an object to a blood source; they can produce both forward and backward spatters
transfer stains
consist of wipes, swipes, and contact/pattern transfer stains; wipes are a result of an object moving through a preexisting bloodstain
swipes
occur when a bloodied object moves across and transfers blood to a target
latent stains
not visible and need chemical enhancements to be seen
projected stains
from arterial spurts or gushes
cast-off stains
occur when blood is released from or projected onto a surface from a bloody object that is in motion; bloodied baseball bats and knives when swung give rise to these stains, which are typically very narrow or occur as "tramlines" when blood is projected from both sides of the weapon in motion
expirated stains