Exam 5 Flashcards
Bloodstain Pattern Analysis: Definition
Study of “static” bloodstains.
Normally associated with aftermath of a violent event.
Provide information specific to events occurred.
Bloodstain Pattern Analysis: Explanation Provided
Provides the “what” instead of “who” of the crime.
Ability to define events that could/not have occurred during bloodshed.
Bloodstain Pattern Analysis: Determinations
Direction a stain was traveling.
Angle of impact.
Distance above a target surface the stain originated.
Type of force used.
Number of blows.
Position of suspect or victim during attack.
Bloodstain Pattern Analysis: History
Referenced from as far back as 1894 Germany.
1950’s US impact angle research begins.
Early 70’s Herbert MacDonnel.
1983 International Association of BPA formed.
Herbert MacDonnel
“Grandfather” of BPA.
Searched all over the world and through history for information and research on BPA then compiled it into a book in early 70’s.
Bloodstain Pattern Analysis: Limitations
Requires extensive training and experience.
Should not be done with limited stains, need multiple samples.
Only provides parameters and estimates.
Few true absolutes.
Bloodstain Pattern Analysis: Experimentation
BPA is reproducible phenomenon.
Same physical laws apply to blood s fluid.
Conduct experiments to achieve similar and predictable results.
Bloodstain Pattern Analysis: Physics
Surface tension, viscosity, gravity, and laws of physics apply equally.
Don’t need to understand physics, just recognize result.
Shape of Blood Droplets
Retain spherical shape in flight due to:
Surface tension.
Molecular bonding causes liquid to occupy smallest possible space (sphere).
Retains shape until acted upon by other forces.
If not a sphere, could not calculate trajectory.
Characteristics of Blood Droplets
Keeps volume, stays together.
Does not spontaneously degenerate from low velocity droplets to fine mist.
BPA Contact Surfaces
Target surface most critical element.
Smoother surfaces provide most usable stains.
Rougher surfaces cause stains to distort.
Distorted stains eliminate value of stain for deciphering information.
Uses of Bloodstain Evidence
Directionality.
Impact angle.
Type of force.
Number of blows struck.
Bloodstain Pattern Directionality: Primary Stains
Inertia caused by motion of droplet forces wave of blood to form.
Wave wells up on opposite point from where stain struck.
Stain points to direction of source.
Bloodstain Pattern Directionality: Secondary Stains
If wave breaks off parent stain, a satellite is formed.
Satellite stain will point back towards parent stain.
Blood to Surface Contact
When blood hits an object, it does not explode, it runs out.
Creates a right angle at contact.
Triangle exists between target surface and line of travel.
Mathematical principles used to determine impact angle.
Bloodstain Pattern: Angle
Elliptical stains most helpful for calculating angles.
Correlating impact angles of several stains creates umbrella below which incident must have occurred.
Bloodstain Pattern: Quantity
Using a number of well-formed stains help establish pararmeters under which the stain was created.
Well-formed Stain
A stain if divided along it’s axis the opposite sides are approximately equal.
Characteristics of Blood in Motion
Blood does not travel in straight line (parabola effect).
Angle at which blood travels can increase but never decrease.
Can decrease in speed but never increase.
Bloodstain Pattern: Force
Low velocity.
Medium velocity.
High velocity.
Bloodstain Pattern: Low Velocity
Result of normal gravitational force.
Energy of 5 ft. per second.
Size of spatter relatively large, 4 mm or larger.
Passive bleeding (nose, cut finger, etc).
Helps track movement.
Bloodstain Pattern: Medium Velocity
Result of force or energy in excess of 5 ft. per second to no more of 25 ft. per second.
Size of spatter ranges between 1-4 mm.
Typical of blunt force trauma.
Bloodstain Pattern: High Velocity
Result of force or energy in excess of 100 ft. per second.
Stains mist in size ranging from 1 mm or less in size.
Usually result of gunshot injuries.
High Velocity Exclusions
Expiratory blood.
Continued explosion.
High speed machinery.
Expiratory Blood
Spitting out blood.
Blood is deluded with air bubbles and other liquid.
Bloodstain Pattern: Velocity Overlap
No specific separation between velocities.
Some overlap exists.
Bloodstain Pattern: Velocity
Refers to speed of instrument creating injury and NOT the speed of blood in flight.
Bloodstain Pattern: Number of Blows
Relies heavily on cast off stains.
Count cast off stains to help determine number of blows.
Add one as the first blow is unlikely to have much excess blood for casting off.
Cast Off Stains
Help determine number of blows in blunt force trauma injuries.
Produced from blood coming off swinging object.
Occur as trails.
Counting cast off stains and grouping them into forward and backward swings make number of blows apparent.
Possible to tell which hand was used.
Can get on back on perp.
Bloodstain Pattern: Size
Helps determine velocity.
Helps give guess as to what object was used.
Bloodstain Pattern: Reconstruction Phenomenon
Void effect or ghosting.
Transfer patterns.
Skeletonization.
Bloodstain Pattern: Skeletonization
Blood begins to dry in 50 seconds.
Blood dries from the outside in.
A ring begins to form on outer edge of droplet, which is skeletonization.
Bloodstain Pattern: Void Effect / Ghosting
Something has been removed that had blocked path of blood to target surface.
Bloodstain Pattern: Transfer Pattern Tyoes
Wipe.
Swipe.
Transfer.
Bloodstain Pattern: Wipe
Run object through blood.
Example: Using clean cloth to wipe up blood.
Bloodstain Pattern: Swipe
Blood-covered object is wiped on something else.
Less blood is seen.
Example: Bloody knifed wiped on towel.
Bloodstain Pattern: Transfer
Bloodied surface comes in contact with another.
Example: Bloody shoe prints, hand prints, hair swipe.
Bloodstain Pattern Analysis: Cautions
Do not make evaluation based on only one stain.
Not always possible to obtain all types of info needed.
Conclusion must be considered against the relationship of all other evidence.
Won’t understand everything, find what you do and start there.
Bloodstain Pattern Analysis: Documentation
Notes.
Sketches.
Photographs.
Video tape.
Bloodstain Pattern Analysis: Presentation/Analysis Methods
Powerpoints. Video tape. Projection sketch. Stringing. Experimentation. Computer software.
Bloodstain Pattern Analysis: Photography
Overall 360 degree shots.
Establishing shots with obvious landmarks.
Close-ups, 90 degree angle.
With and w/o scales.
Bloodstain Pattern Analysis: Photography Close-ups
Macro lens.
2 photographs, with and w/o scales.
2 scales for width and length.
90 degree photographs.
Bloodstain Pattern Analysis: Video Tape
Allows for different perspectives.
Enhances relationship of evidence to scene.
Can add quick narration.
Bloodstain Pattern Analysis: Projection Sketch
Incorporates all intrinsic parts of evidence.
Bloodstain Pattern Analysis: Stringing
Run strings from stains based on direction to find point of origin.
Provides graphic illustration of where stains originated.
Bloodstain Pattern Analysis: Recovering Evidence
Use fingerprint method for lifting stains.
Dried blood scraping for serology testing.
Cotton swabs to collect wet blood.
Bloodstain Pattern Analysis: Bio-hazards
Aids virus.
Hepatitis B.
Wear protective clothing.
Use common sense.
Bloodstain Pattern Analysis: Aids Virus
Can survive in liquid state for 15 days.
Refrigeration or frozen increases survival.
Once dried becomes inactive.
1 to 9 ratio of bleach to water mix kills virus in 1 minute.
Digital Evidence: Key Facts
- Many types of crimes involved.
- Every crime scene is a digital crime scene.
- Can be fragile.
- Can be easily altered.
- Never assume it is destroyed.
Digital Evidence: Types of Crimes
Everything from computer to violent crimes.
Information stored on many different devices.
Digital Evidence: Crime Scene
Can be involved in every crime scene.
Storage devices and electronics like thumb-drives, sim cards, printers, GPS, cars, cameras, etc.
All can be found/hidden at crime scenes.
Look for digital evidence in places you’d never think to look (legos!).
Digital Evidence: Physical Cautions
Evidence often very fragile.
Susceptible to magnets, extremes in hot or cold.
Digital Evidence: Digital Cautions
Easily altered (just turning on computer can change files). Dates, names, content easily changed.
Criminal Uses of Digital Devices
Target of crime.
Instrument of crime.
Repository of evidence documenting crime.
Computers as Target of Crime
Stealing information.
Identity theft.
Computers as Instrument of Crime
Stalking through internet, GPS, etc.
Hacking.
Transactions and communication.
Computers as Repository of Evidence
Fake IDs, drug trafficking info, etc.
Computers can help create timelines for crimes.