Bloodstain and Spatter LabBackground:

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 glass square masking tapecomputer paper concrete block/brick cardboard

piece of clothing plastic bagcalipers

newspaper or butcher paper 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.”

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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. Observe the patterns, measure the diameter of the droplet with the calipers and record this information in Data Table A. When measuring, ignore the “satellites” that spurt out from the drop; just measure the circle.

6. Write your groups’ cardboard data on the white board and be sure to record the class data before you leave. 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 Ms. Bolton when you are ready. You will need to share your data 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. Turn in the labeled computer paper to Ms. Bolton with all group names written on it. You will use the cardboard in experiment #2.

9. Clean the calipers if you got blood on them. You may move onto experiment #2 once Ms. Bolton has checked your lab station.

Experiment 2: Bloodstain Shape vs. Angle of ImpactThe 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 meter stick/rulercalipers clipboard protractornews paper or butcher paper masking tape 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.

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.

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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. Write your averages on the board and be sure to record the class data before you leave.

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Ending point

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 Butcher paper CalculatorMarker or chalk Tape measure 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.

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Starting point

d

Aerial view of concrete walkway or butcher paper

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.

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Trigonometric Equations

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 stainE’ to F’ = width (w) of blood stainA’ to B’ = length (l) of blood stainblood drop in space (assume spherical) therefore EF = AB

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A

B

F

E

B’

F’

E’

A’

Mathematical relationship between blood stain and angle of impact

Determination of Point of Origin in Space

Solve for the length of Z (D to B). hint: (angle of impact) is known, and Y is given.

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A

B

BA

D

pt of origin in space

Z

Y

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 Calipers ProtractorString Ring stand Blood spatter evidenceTrig calculator

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.

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spot # W (cm) L (cm) W / L angle impact (sine) Y (cm) Z (cm)

Y = distance from base of individual droplets to the PI

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W

L

S2

S1

PI

L

S2

S1

PI

PI

Y2

figure 1blood spots at crime

scene

figure 2 bisect blood droplets & draw a line to the

PI

figure 3

measure and record the width & length of

each blood droplet

figure 4

measure distance from droplet to PI

Y1