Bloodstain Pattern Analysis (7.2)
Blood drops
Bloody nose
Cut finger
Circular drops that are large in diameter
Tear shaped due to shaking off the blood.
NAS Report
For crime scene reconstruction, it is important to have knowledge of bloodstain patterns
Find bloodstains at homicide scenes, burglary, assaults, and car accidents.
Successful reconstruction through bloodstain patterns involves knowledge in many topics
knowledge in related scientific topics
understanding of correct terminology
knowledge in math and significant figures
Knowledge in the physics behind the transfer of fluids
wound pathology knowledge
Skills in analysis of general bloodstain patterns
Guides
There are many guides to thoroughly look at to understand this topic
Reconstruction
How to document bloodstains
How to enhance bloodstain patterns not visible by the naked eye
Various bloodstain pattern characteristics
How to tell direction of the blood drop
In flight and in motion blood drop dynamics
Terminology
You should always try to recreate the bloodstain. Experience is key to being successful in bloodstain analysis
Knowing how to analyze bloodstain patterns will help an investigator to determine what did or did not happen at the crime scene
What to do at a scene
Relax and don't over exaggerate
Know how much blood is in the human body
Knowing this will help you give an accurate description of the scene.
Females: 4-5 Liters
Males: 5-6 Liters
Visible Bloodstains
Presumptive color tests
hemastix
Phenolphthalin reagent
Color change indicated possible blood. A swab will be taken to the crime lab who will then run a confirmatory test for human blood
Latent Bloodstains
Leuco crystal violet
amido black
If someone knows the chemistry and physics behind these tests, they are reliable
Reacts with hemoglobin in blood. Will give a color of violet or dark blue
Permanent color change
.
False Positive
Luminol: Rust
ABAcard HemaTrace: ferret blood and higher primates
Risks
Blood borne pathogens
HIV
Hepatitis
More of a risk of contracting
PPE
Eye shield, face mask, tyrek suit, gloves, and shoe coverings
Information given by evidence
What direction the blood drop was traveling
The angle that the blood drop was dropped from
Approximately where the blood drop originated from
What type of force was used and what direction it was applied (Mechanisms that blood spatter is created
Number of impacts
Approximate location of the suspect, victim, and various objects
Sequence of events
Left or right hand impact?
By analyzing the tail of blood drop, you can determine the angle and direction of impact
Investigators will create a card that has reference droplets at angles between 10 and 90 degrees
location, size, and shape of the bloodstain can help determine if the drops happened during the same event
With more force, you will see smaller blood drops
High-velocity/high energy spatter
Blood due to a gunshot, small drops (1mm)
medium velocity impact spatter
Blood due to a beating or stabbing (1-4mm)
low velocity spatter
Blood due to a bloody nose (>4mm)
Types of bloodstains
Passive
gravity
Due to blood drips, flowing blood, blood pools, and splashes of blood
Impact spatter
object --> source of blood
forward spatter and back spatter
transfer stains
Due to swipes and wipes and direct contact
Latent
Can't see with the naked eye and have to use chemicals to enhance
Other
Projected
Gushes of blood and spurts from arteries
cast-off
An object in motion that has blood on it will release blood. Example: baseball bat and knife with blood on them
Reconstruction