9th Grade Forensic Science
T. Trimpe 2006 http://sciencespot.net/
What is BPA? Bloodstain Pattern Analysis
How can an investigator use bloodstain patterns to analyze a crime scene?
• Location and description of individual stains and patterns
•Direction a blood droplet was traveling by calculating angles of impact
•Area of origin of blood source or sources
•The type of object used in attack (edged, blunt, firearm, etc.)
•Minimum number of blows
•The positions of the victim, suspect, and objects during events
•The sequence of events
Evidence from bloodstain pattern analysis is not usually powerful enough on its own
to convict someone of a crime, but it can be useful in supporting other types of
evidence found at a scene.
How does a blood droplet
form? Click the image
for an animation.
http://www.crimescenetwo.com/img/popup/book2p2.jpg
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.
• 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
form the spatter; can help determine the direction from
which the blood traveled.
Satellite Spatters
Spines
Parent Drop
• 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
– Low, medium, or high impact spatters, cast-off, arterial
spurting, expiratory blood blown out of the nose,
mouth, or wound.
• Transfer or Contact Bloodstains
– The pattern created when a wet, bloody object comes
in contact with a target surface; may be used to
identify an object or body part.
– Wipe pattern from an object moving through a
bloodstain or swipe pattern from an object leaving a
bloodstain.
Images from http://www.bloodspatter.com/BPATutorial.htm
Luminol
• Used by crime scene investigators to locate traces of blood, even if it
has been cleaned or removed.
• A luminol solution is sprayed throughout the area under investigation.
• The iron present in any blood in the area causes the chemical reaction
that leads to the blue luminescence revealing the location of the blood.
•Any glow detected may be documented by a long exposure photograph
as the glow only lasts 30 seconds.
• Luminol only shows investigators that there might be blood in an area, since it also reacts
to some metals, paints, cleaning products and plant matter. A specialist can tell the
difference in the chemical’s reaction to each substance, and then perform more tests to
determine whether the blood is human.
•Luminol also can point the way to other evidence or how events might have unfolded at a
crime scene. If it is sprayed on a carpet and produces a glow, officers might peel back the
rug to reveal a floorboard soaked with blood. It might also show the direction in which a
criminal walked or dragged a body, or whether the victim was shot from behind or above.
•One problem with luminol is that the chemical reaction can destroy other evidence in the
crime scene. For this reason, investigators only use luminol after exploring a lot of other
options
Page 239
Calculator on pg.
242
Blood Spatter Labs
• You will be creating sample drop patterns using single drops and
multiple drops. We will also investigate the effect of motion and the
angle of impact on blood spatter.
• This can be messy! Be very careful to keep the blood on the paper
and not on yourself, the table, or floor.
• Hold you hand as steady as possible when making the drops.
Brace your wrist against the meter stick to help you.
• Get your materials from your teacher – poster board, black marker,
meter stick, goggles, apron and a bottle of blood.
If you make a mess, clean it up immediately!
Blood Spatter: Single Droplets
• You will be creating sample drop patterns created by blood dropping from 4
different heights.
• This can be messy! Be very careful to keep the blood on the paper and not on
yourself, the table, or floor. Allow the blood to dry before you move the paper.
• Label the top of the poster board “Single Droplets.
•Draw and label you poster board as shown below
•Put all lab members name on back
•
Single Drop Analysis
• Now that your blood samples are dry, it’s time to do some measurements.
• Use the vernier caliper to measure the diameter of each droplet. If there are
spines or protrusions on the drop, don’t include those in your measurement.
Don’t measure the spines – just
the diameter of the main area of
the droplet.
• Record your measurements in the chart on your worksheet, find the average for
each height, and answer the questions.
Blood Spatter: Multiple Droplets
• You will be creating sample drop patterns created by three droplets landing the same
location from 4 different heights.
• This can be messy! Be very careful to keep the blood on the poster board and not on
yourself, the table, or floor.
•Label the top of the poster board “ Multiple Droplets”.
•Draw and label you poster board as shown below
•Put all lab members name on back
•Write P= and S= smaller in the box
Multiple Drop Analysis
• Now that your blood samples are dry, it’s time to do some measurements.
• Use the vernier caliper to measure the diameter of each droplet. If there are
spines or protrusions on the drop, don’t include those in this measurement.
• Measure the diameter of the spread – greatest distance between the satellite
Don’t measure the spines – just
the diameter of the main area of
the droplet.
• Record your measurements in the chart on your worksheet, find the averages,
and answer the questions.
Blood Spatter: Motion Droplets
• During this lab, you will see how motion affects the size and shape of the droplets and
spines. You will need a long piece of butcher paper (4-5 meters in length) and tape to secure
it to the floor. You will also need safety goggles.
• To do the lab, you will need to hold the dropper bottle upside down so that your hand is out
and away from your body (waist level), but is still over the paper.
• Start off walking at a SLOW WALKING RATE along the paper strip from one end to the
other and GENTLY squeeze the bottle as you walk so that blood is released ONE DROP at a
time. Be sure that all the drops land on your paper strip.
•Repeat this procedure using a NORMAL WALKING RATE and a FAST WALKING
RATE.
Miss the paper? Use a paper
towel to wipe it off the floor!
Walking Direction
Motion Drop Analysis
•
•When you are done with each test, draw a sketch of the blood droplets
on your worksheet. Answer the questions after you have finished all
three tests. Clean up your area and put away your materials.
Lab 4: Angle of Impact
• You will be creating sample drop patterns created by droplets landing at
different angles from the same height.
• Cut and label 4 pieces of poster board the - 15o, 30o, 45o, 60o, or 75o.
• Place the first piece of paper on the clip board and align the clipboard with the
15o line. Hold the bottle of blood at a height of 50 centimeters from the top of the
table.
• GENTLY squeeze the bottle so that ONE drop of blood is released and lands on
the paper. Repeat two more times at this angle.
• Continue testing by dropping blood from a height of 50 centimeters at each of
the other angles.
• When you are done, answer the questions
on your worksheet. Clean up your area and
put away your materials before you leave
class.
Clipboard &
Paper
Height of
50 cm
Angle
Guide
Blood Spatter: Angle of Impact
• You will be creating sample drop patterns created by droplets landing at
different angles from one drop height.
• This can be messy! Be very careful to keep the blood on the paper and not on
yourself, the table, or floor. Allow the blood to dry before you move the paper.
• Cut 4 pieces of poster board the same size as the angle board
• Set up the angle guide near the end of the table as shown below. Write your
names on the four pieces of paper and indicate the angle for each test - 20o, 40o,
60o, and 80o.
Clipboard/Paper
Angle Guide
•Place the first piece of paper on the clip board and set it at a 20o angle from the
table. Hold the bottle of blood at a height of 50 centimeters from the top of the
table.
• GENTLY squeeze the bottle so that ONE drop of blood is released and lands on
the paper. Repeat two more times at this angle.
• Continue testing by dropping blood from a height of 50 centimeters at each of
the other angles.
• When you are done, leave your paper to dry overnight. Clean up your area and
put away your materials.
25o
Trial 1 Trial 2 Trail
3
http://www.fbi.gov/publications/leb/2005/feb2005/feb2005_img_29.jpg
Angle of Impact Analysis
• Now that your blood samples are dry, it’s time to do some measurements.
• Use the ruler to measure the length and width of each droplet. If there are
spines or protrusions on the drop, don’t include those in this measurement.
• Record your measurements in the chart on your worksheet, find the averages,
and answer the questions.
Which of the three blood droplets shown would have been
created by a wound in the lower part of the leg? Explain.
If you have a blood droplet as shown at left, what does it tell you?
Explain.
If you find a trail of blood with droplets that are close together, what could this
mean?