Forensic Science Lab Activity
Warning: Some material in this presentation and
related videos may be too graphic for some people.
T. Trimpe 2006 http://sciencespot.net/
What does the abbreviation BPA represent? Bloodstain Pattern Analysis
What can an investigator learn from the analysis of a blood spatter?
 Type and velocity of weapon
 Number of blows
 Handedness of assailant (right or left-handed)
 Position and movements of the victim and assailant during and after the attack
 Which wounds were inflicted first
 Type of injuries
 How long ago the crime was committed
 Whether death was immediate or delayed
Source: http://science.howstuffworks.com/bloodstain-pattern-analysis1.htm
http://www.crimescenetwo.com/img/popup/book2p2.jpg
Detecting Blood Evidence
• Light Source
• Investigators will first examine the crime scene
to look for areas that may contain blood.
• Use a high-intensity light or UV lights to help
them find traces of blood as well as other
bodily fluids that are not visible under normal
lighting conditions
Detecting Blood Evidence
• Blood Reagent Tests
– presumptive tests
– detect blood at crime scenes based upon the
properties of hemoglobin in the blood.
– Further tests at the crime lab can determine if it is
human blood or not.
Blood Reagent Tests
Kastle-Meyer test
• Uses chemical
phenolphthalein
• Produces a pink color
when it reacts with
hemoglobin
HemaStix
• Uses a strip coated with
tetramethylbenzidine (TMB)
• Produces a green or bluegreen color in the presence
of hemoglobin
Detecting Blood Evidence
• Chemical is used to locate traces of blood, even
if it has been cleaned or removed.
• Reacts with the iron present in blood and causes
a blue luminescence.
• Disadvantages:
– Can reacts with other substances (paints, cleaning
products, plant materials, some metals)
– Chemical reaction can destroy other evidence in the
crime scene.
Detecting Blood Evidence
Fluorescein
• Chemical capable of
detecting latent or old
blood, similar to luminol.
• UV light and goggles
are used to detect any
illuminated areas after
stain is sprayed
• Stains appear greenishwhite if blood is present.
Detecting Blood Evidence
Leuco Crystal Violet
or LCV
• chemical process that
is used for blood
enhancement
• helps to make the
blood evidence more
visible so it can be
photographed
and
analyzed.
Video Clip
Click picture for video
Blood Stain
Pattern Analysis
Blood Stain Pattern
Analysis
• The bloodstain patterns left by falling,
projected or smeared blood can be
analyzed by trained crime scene
investigators.
• Careful observation and measurement of
the position and shape of bloodstains can
give lots of information about the direction
of travel, angle of impact and the speed or
velocity of the blood droplets.
Types of Bloodstain Patterns
• Passive Bloodstains
– Patterns created from the force of gravity
– Drop, series of drops, flow patterns, blood pools, etc.
• Projected Bloodstains
– Patterns that occur when a force is applied to the
source of the blood
– Includes low, medium, or high impact spatters, castoff, arterial spurting, expiratory blood blown out of
the nose, mouth, or wound.
• Transfer or Contact Bloodstains
– These patterns are created when a wet, bloody object
comes in contact with a target surface; may be used to
identify an object or body part.
– A wipe pattern is created from an object moving
through a bloodstain, while a swipe pattern is created
from an object leaving a bloodstain.
Images from http://www.bloodspatter.com/BPATutorial.htm
Bloodstain Pattern Analysis Terms
• Spatter – Bloodstains created from the application of force to the area
where the blood originated.
• Origin/Source – The place from where the blood spatter came from or
originated.
• Angle of Impact – The angle at which a blood droplet strikes a surface.
• Parent Drop – The droplet from which a
satellite spatter originates.
• Satellite Spatters – Small drops of blood
that break of from the parent spatter when
the blood droplet hits a surface.
• Spines – The pointed edges of a stain that
radiate out from the spatter; can help
determine the direction from which the
blood traveled.
Satellite Spatters
Spines
Parent Drop
Traveling Blood Droplets
• When a force is applied to a mass of
blood, the blood breaks into droplets
• The droplets fly through the air as “perfect”
spheres due to surface tension
Surface tension
enables blood droplets
to maintain a sphere
shape.
Stages of impact
Stage 1: contact &
collapse
Image used with permission from Tom Bevel & Ross Gardner, June 2006.
Stage 2: displacement
Image used with
permission from Tom
Bevel & Ross Gardner,
June 2006.
Stage 3: dispersion
Image used with permission
from Tom Bevel & Ross
Gardner, June 2006.
Stage 4: retraction
Image used with
permission from Tom Bevel
& Ross Gardner, June
2006.
Stages of Impact Video
Click picture
to review
stages of
impact
Height and size of blood drops
• A blood droplet released from a
1m height will be smaller than a
blood droplet released from a
1.5m height.
• Higher height = higher velocity =
larger droplet
• This is because the velocity of the
blood droplet released from a
higher height is greater.
Surface and shape of
blood drops
Images courtesy DUIT Multimedia: Paul Ricketts.
Low impact
• Low impact is really blood under the
influence of gravity - it just falls.
Velocity:
5 f/s, 1.5 m/s
• Free-falling drops (gravity only)
• Cast off from fist, weapon, etc.
• Dripping (blood droplets into themselves)
• Splashing (stepping, throwing, etc.)
• Arterial spurting
Image courtesy UWA PhD research student Mark Reynolds.
Arterial spurting
Medium impact
• Medium impact occurs when a force
such as a bat is applied.
Velocity:
25 - 100 f/s, 7.5 - 30 m/s)
Image courtesy UWA PhD research student Mark Reynolds.
High impact - fine
mist of droplets
Velocity:
>100 f/s,
>30 m/s
Gun shot or
machinery
Image
courtesy
Stuart
James,
February
2007
Angle of impact
Image used with
permission from
Stuart James,
February 2007.
Angle of Impact Animation
Click
picture for
animation,
then click
on angle of
impact tab
Determining
Direction of Blood



The angle can be determined
mathematically.
Width/Length, then take the
inverse sin (sin-1).
This number is the impact
angle (90 = perpendicular to
surface; <10 at a sharp angle)
Determining Point of Origin
©2010 Elsevier, Inc.
Dexter explains Blood Spatter
Click picture for
video
Reconstructing
the crime
• With the evidence that is collected, the
crime scene investigator attempts to
reconstruct the crime.
• This involves trying to work out what events
happened and the order that they happened.
Image courtesy UWA
PhD research student
Mark Reynolds.