Download Blood Spatter Pattern Station #2: Height to Blood Spot Diameter

Bloodstain and Spatter Lab
Background:
One technique used by crime scene investigators is the analysis of
stains left by blood shed at a crime scene. Bloodstain pattern analysis can
be a powerful forensic tool used in investigations. If the forensic scientist understands
the dynamics of the altercation, how blood behaves when it exits the body, and how it
reacts when it contacts a surface, then an attempt can be made to understand what
happened and to determine if a crime occurred. The trained investigator looks at the
patterns made by shed blood and tries to determine what did and/or what did not happen.
Interpreting blood stain patterns involves physical measurement of blood droplets, pattern
recognition using photographs or experiments, the use of trigonometry, and the
knowledge of physics of motion. Together, with the other types of evidence at the scene
(fingerprints, tool marks, footprint impressions, DNA evidence, chemical analysis, etc.)
the forensic scientist pieces together the puzzle to re-create a logical sequence of events,
which is supported by the evidence. Collecting and documenting the evidence correctly
is another skill which is just as important as interpreting the evidence. Bloodstains cannot
always be carried back to the lab, so care in documenting the scene is of utmost
importance. Photographs and detailed sketches drawn to scale are invaluable tools that
help piece together the puzzle.
Purpose:
You will be introduced to the basics of bloodstain pattern analysis. The
experiments will ask you to produce typical bloodstain patterns commonly found at a
crime scene where blood has been shed. You will then sketch and document the patterns
found in each activity. Attention to detail is imperative, so that you will have an accurate
reference sheet when it comes time for the mock crime scene at the end of the semester.
Experiment 1: Surface Studies – Vertical Drips on Various Surfaces
Materials:
“Drip/Projected” blood
computer paper
piece of clothing
newspaper or butcher paper
glass square
masking tape
concrete block/brick cardboard
plastic bag
calipers/ruler
2 meter sticks or a tape measure
CAUTION: the edge of the glass is very sharp! Wrap a piece of masking tape on the
edge that you are going to hold and only touch that side.
Procedure:
1. Lay a piece of newspaper or butcher paper down over your work surface. Any
blood spilt on the table or floor must be clean IMMEDIATELY.
2. Using the cardboard as the target surface, hold the dropper bottle in a vertical
position so that the dropper is exactly 1 ft above the target surface (cardboard).
3. Gently squeeze the bottle so that ONLY one drop is released from the bottle at the
1 ft height and lands on the target surface. Label this drop “1 ft.”
1
4. Move the dropper to a vertical distance of 2 ft, 3 ft, 4 ft,
5 ft and 6 ft, making a drop for each height on a
different area of the same target surface. Be sure to
label each drop and height.
5. Allow the cardboard to dry or pat it dry without
disturbing the drop size/shape. Observe the patterns,
measure the diameter of the droplet with the calipers/ruler and record this
information in Data Table A. When measuring, ignore the “satellites” that spurt
out from the drop; just measure the circle.
6. Fill in your groups’ cardboard data on the class Google sheet (Analysis #1) and be
sure to record the class data on your data sheet. You’ll need this information for
the analysis section.
7. Repeat steps 1-5 using one of the other target objects: paper, glass square,
concrete block, plastic bag, or the piece of clothing. Get this from Mrs. C when
you are ready. You will need to share your data on the Google sheet and observe
other groups’ experiments so you can complete all of Data Table A.
8. Rinse the blood off the glass, bag, clothing, and brick after all groups have made
their observations. You will use the cardboard in experiment #2.
9. Clean the calipers/rulers if you got blood on them. You may move onto
experiment #2 once Mrs. C has checked your lab station.
For homework, graph the data from analysis #1 and answer the questions on the data
sheet.
Experiment 2: Bloodstain Shape vs. Angle of Impact
The objective of this experiment is to study the oval or elliptical nature of the
bloodstains produced by drops of blood falling 24 inches onto non-horizontal surfaces
compared with blood drops falling onto a horizontal surface (exp. 1).
Materials:
“Drip/Projected” blood
cardboard
calipers
clipboard
news paper or butcher paper masking tape
meter stick/ruler
protractor
calculator
Procedure:
1. Lay a piece of newspaper or butcher paper down over your work surface. Any
blood spilt on the table or floor must be clean IMMEDIATELY.
2. Blot any un-dried blood on your cardboard
and put that side face-down on the clipboard.
3. Tape one end of the clipboard to the table by
making a hinge out of tape. The clipboard
should be right at the edge of the table.
4. Hold the protractor to the edge of the
clipboard so that the protractor is
perpendicular to the table top and aligned to that the center to the protractor is at
the edge of the hinge-end of the clipboard.
2
5. Set the angle of the board using the protractor so that the board will have the
correct angle of impact: 0o, 10o, 30o, or 60o. You will start with 0o, so the board
should be flat on the table.
6. Just as in experiment #1, you will dispense one drop of blood from 2 ft, making
sure it hits the cardboard. One partner will hold the clipboard at the correct angle,
another will drop the blood, and another will label the drops as they are made. If
you have a 4th person, their job is to watch to make sure the dropper bottle stays at
a constant height and that the angle of the clipboard is correct.
7. Keeping the height constant, repeat this two more times at 0o.
8. Allow the drop to dry and record the width and length in Data Table B. Record
just the main body of the drip.
9. Keeping the height constant, repeat steps 5-8 for the remaining angles, 10o, 30o,
and 60o. Be sure to complete three trials for each angle.
10. Calculate the average width-to-length ratio (width divided by length) and record it
in Data Table B to the nearest hundredth. Enter your averages on the Google
sheet and be sure to record fill in Data Table C after all groups have entered their
data.
3
Experiment 3: Speed of Moving Blood Source
Purpose: Analyze the distance between blood drops to determine the
speed of the moving blood source. Remember the formula to
determine speed is distance/time.
Materials:
Valved-burette filled w/fake blood
Marker or chalk
Butcher paper
Tape measure
Calculator
Stopwatch
Procedure:
1. Fill a chemistry burette with fake
blood
2. Go outside on a dry concrete
surface and measure off a distance
of 15 ft or cut 15 ft of butcher
paper.
3. Place the burette spigot in your hand
proximal to your fingers and hold it in a
normal walking motion.
4. Position yourself at the zero mark of the
distance you will cover.
5. Have another person in your group be
the designated timer.
6. Select another person to mark the drops
as they each hit the surface.
7. Adjust valve on the burette so the drip
rate is about 1-2 drops per second.
Starting point
Ending
point
d
Aerial view of concrete walkway or
butcher paper
4
8. Once you have been given the “GO”
command from the timer, walk at a normal
pace dripping the burette liquid over the 15
ft. distance; do not swing the burette (i.e.,
keep it at a 900 angle to horizontal surface).
9. Timer: be sure to stop the time as the
person dropping the liquid reaches the 15
ft. mark. Record the total time it took to
walk the distance.
10. Calculate the width-to-length ratio for
each drop and record this information on
your data sheet.
11. Repeat this process but change the pace
to a faster walk or run. If you haven’t
marked the spots from the 1st trial, do that
now so you can tell the 1st trial’s spots from
the 2nd trial’s spots.
1. Complete Analysis questions #1-2.
13. Ask another two groups to share
their speed and width-to-length ratios
for one of their trials. You will need
this for Analysis #3 & 4.
5
6
Trigonometric Equations
Mathematical relationship between blood stain and angle of impact
A
E
F
E’
B
A’
B’
F’
A,B, E, F = four points on the surface of sphere (blood drop in space)
A’,B’, E’, F’ = same four points projected on a surface in the form of a blood stain
E’ to F’ = width (w) of blood stain
A’ to B’ = length (l) of blood stain
blood drop in space (assume spherical) therefore EF = AB
7
Determination of Point of Origin in Space
A
B

D
A
’
B
’
pt of origin in space
Z

Y
Solve for the length of Z (D to B). hint:  (angle of impact) is known,
and Y is given.
8
Process for determining spatial origin of blood source
1. Bisect at least three (3) blood droplets that will result in a point of intersection (PI) &
label each droplet respectively i.e., S1, S2, S3, etc.
2. Using calipers, measure width & length of each droplet identified in the previous
step.
3. Determine angle of impact of each of the blood spots (sine function)
Sine = O/H = W/L = angle of impact
4. Measure distance (Y) of blood drop to PI for each droplet.
5. Determine Z (distance from floor or wall) using tangent function
Tangent = O/A = Z/Y or Z = tangent * Y
6. String distance using appropriate materials
Experiment #4: Blood Stain Address Lab
Purpose: Determine the address of the blood source given blood spatter evidence
Materials:
Ruler
String
Trig calculator
Calipers
Ring stand
Protractor
Blood spatter evidence
Procedure:
1. Construct the data on a separate sheet of paper (see below).
2. Locate a series of blood droplets that can be measured (W & L) and have a common
point of intersection (PI). Tape 2 additional pieces of paper to the sheet to bisect.
3. Line up the droplet w/ a ruler so it bisects (runs down the middle) the drop.
4. Once aligned, draw a pencil line starting through the droplet to the “PI” (this will
need to be estimated). Repeat this process for other blood droplets until the point of
intersection (PI) or line of convergence is established.
5. Using calipers measure the width and the length of each identified droplet (0.01 cm)
6. Divide the width by the length and record (Remember sine = O/A = W/L = of
impact). Using a calculator, determine the angle of impact and record in table.
7. Measure the distance (cm) from the droplet to the PI and record.
8. To determine Z (position in space) = tangent of  impact * Y (distance from the
droplet to the PI ). Repeat for the other spots and record.
9. Once all the calculations have been performed, string the flight path of the droplets to
determine the origin in space. Use the protractor the set the angle then tie a string
onto the ring stand (or use tape) to secure it.
9
spot #
W (cm)
L (cm)
W/L
angle impact (sine)
Y (cm)
Z (cm)
Y = distance from base of individual droplets to the PI
figure 1
blood spots at crime
scene
figure 2
bisect blood droplets
& draw a line to the
PI
PI
figure 3
measure and record
the width & length of
each blood droplet
S1
S2
L
PI
W
L
figure 4
measure distance
from droplet to PI
S2
Y1
S1
PI
Y2
10