FORS-2107EL Study Guide - Winter 2018, Comprehensive Midterm Notes - Chromatography, Vacuum, Solvent
12 Oct 2018
School
Department
Course
Professor
FORS-2107EL
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Forensic Science - Day 1 2018.01.08
Bloodstain Pattern Analysis
-BPA is the study of the shapes, sizes, and locations of bloodstains in order to
determine the physical events which gave rise to their origin
History
-1895: Dr. Eduard Piotrowski published first reference to BPA, in Poland
-1939: Dr. Victor Balthazard the first ti use physical interpretations of stains
Forensic Importance
-What we are looking for in a forensic sense:
-Location of original blow
-Number of blows
-Type and velocity of weapon used
-Movement and directionality of assailant/ victim/ objects, while they were shedding
blood
-Position of assailant/ victim/ object during bloodletting
-If an artery was cut
Investigative Importance
-What we are looking for in an investigative sense:
-Prove or refute statements by suspects/witnesses
-Correlation with pathology/laboratory findings
-Ultimate goal of reconstructing the crime scene:
-Who, what, when, where, why, how
Basic Principles of BPA
-1) Blood will behave according to the law of physics
-2) The size of a projected bloodstain has a direct relationship to the speed at which it
is traveling
-3) You can tell the direction a bloodstain was moving by its shape
-4) Bloodstain patterns are predictable and reproductive
Key Terms and Concepts
-Properties of blood
-Stages of impact
-Categories of bloodstains
-Stain velocity
find more resources at oneclass.com
find more resources at oneclass.com
-Force vs. stain size relationship
-There is passive stains, and ones that have force applied to them
-Directionality
-Angles of Impact
Properties of Blood
-8% of human body weight is blood
-Average 5L in human blood
-Composed of:
-Cells (45%): RBCs, WBCs, and platelets
-Plasma (55%): 92% H2O, proteins, ions, gases, etc.
-6x more viscous then H2O:
-Viscosity is a liquids resistance to change of form or flow due to the mutual
attraction of the molecules to each other
Surface Tension
-The force that pulls the surface molecules, of the drop, towards the interior of liquid
and therefore decreases the surface area
-Larger surface area = greater surface tension
-Droplets of blood in are and spherical not tear drop shaped
-When a force is applied to a mass of blood, it breaks the blood into the droplets that
fly through the air as spheres
-Fingers, weapons, etc. will form different volumes of blood drops due to different
surface area and tension of blood source
Stages of Impact
-1) Contact and collapse (looks like a hat)
-Drop collapses from the bottoms up when it hits
-The drop will be pushed outwards into a rim (like a hat shape)
-2) Displacement (looks wobbly outside rim)
-Dimples and spines begin to form based on the irregularities of the impact surface
-This occurs due to the texture of the surface that the blood is hitting, different
surfaces cause different amounts and patterns of spines
-3) Dispersion (looks like a bowl)
-Most of the volume of blood is forced to the rim
-Creates satellite spatter that fall (flies) off the rim
-Blood falling from a height or high velocity can overcome its natural
cohesiveness and appears as spiking patterns around the original drops
-4) Retraction (looks like final drop shape)
-Surface tension will be trying to keep the droplet together
-Satellite spatters with enough momentum can form completely separate stains
-Droplet can burst if the force pulling it apart is great enough
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Bpa is the study of the shapes, sizes, and locations of bloodstains in order to determine the physical events which gave rise to their origin. 1895: dr. eduard piotrowski published rst reference to bpa, in poland. 1939: dr. victor balthazard the rst ti use physical interpretations of stains. What we are looking for in a forensic sense: Position of assailant/ victim/ object during bloodletting. What we are looking for in an investigative sense: Ultimate goal of reconstructing the crime scene: There is passive stains, and ones that have force applied to them. 8% of human body weight is blood. Plasma (55%): 92% h2o, proteins, ions, gases, etc. Viscosity is a liquids resistance to change of form or ow due to the mutual attraction of the molecules to each other. The force that pulls the surface molecules, of the drop, towards the interior of liquid and therefore decreases the surface area. Larger surface area = greater surface tension.
