Bloodstain Pattern Analysis Exam 1

what are the objectives of BPA?

1. direct scene analysis

2. measuring device

3. clothing

4. autopsy photos

5. reconstruction

what is the goal of reconstruction?

find out what events occurred, who did it, where did the event occurred, who wasn’t there, where is wasn’t, and when did it happen

what is low-velocity blood spatter?

velocity up to 5 feet/second; big blood drops

what is medium-velocity blood spatter?

velocity range 5-25 feet per second; medium sized drops; best for reconstruction

what is high-velocity blood spatter?

velocity greater than 100 feet per second; mist

what are the causes of blood volume loss?

skin- injury (or postmortem)

mouth and nose- cancer, tuberculosis, gunshot wound

respiratory system- injury causing blood to accumulate in airway; frothy appearance

gastrointestinal tract- high: partially digested blood, “coffee ground” emesis; low: rectum, red blood

what are different injuries that can cause blood loss?

abrasions- scraping of the skin

lacerations- skin is torn by shearing or crush; irregular shop

incised wounds- cutting injuries by sharp objects

stab wounds- caused by sharp objects but deeper; more internal bleeding

gunshot wounds- entry wound: have blackish marking around wound; exit wound: skin will be raised

what are the different bloodstain patterns within the body?

postmortem lividity- cessation of blood circulation; red blood cells settle

carbon monoxide/cyanide poisoning- cherry red settling

what is the composition of blood?

plasma- 52-62%

white blood cells & platelets- <2%

red blood cells- 38-40%

pH- 7.4

what are the physical properties of blood?

viscosity- the resistance of a fluid to flow; blood is 4x thicker than water

surface tension- force per unit length; 50 dynes/cm (less than water)

relative density- d = m/v; 1.060 g/cm

adhesion- attractive force between unlike molecules; blood affixed to a wall

cohesion- attractive force between like molecules; a single drop of blood

capillarity- surface tension causes a liquid to be drawn upward in a container

what is the shape of a falling drop?

either elongated, flattened, or ball/sphere

what is drop volume as a function of source?

if a drop is forming on a larger surface, the increased surface area presents an increased surface tension; ex. blood dropping from a bat will form bigger blood drops than from a knife

what are the three broad categories of bloodstain pattern?

passive- no outside forces

spatter- some blood subjected to external forces

altered- physical or physiological alteration

what is the logic tree to bloodstain pattern analysis?

level 1- bloodshed event, bloodstains, is the substance blood?

level 2- evaluate physical characteristics, utilize knowledge of BPA

level 3- evaluate case facts, assess possible mechanisms for bloodstain patterns

level 4- reconstruction of bloodshed event

what is the taxonomy of passive categories of bloodstains?

transfer- swipe and wipe

flow

drops- single, multiple and trail

large volume- free falling, saturation and pool

what is the different between free falling drops on horizontal surfaces versus angular surfaces?

the way the satellite spatters form