Abstract
There is evidence to be gathered at every crime scene. The hard part is making sense of it all. That's where crime scene investigators and forensic scientists come in. In this science fair project, you will investigate blood spatter using fake blood. Your job, as an impartial scientist, is to deliver facts so that justice can be served. Are you up to the challenge?Summary
Michelle Maranowski, PhD, Science Buddies
Thank you to Mr. Geoff Bruton of the Ventura County Sheriff's Department Forensic Science Laboratory for helpful discussion.
- Scotch® is a registered trademark of 3M.
Objective
To simulate a crime scene using fake blood, and predict where the blood-shedding event occurred, using blood-spatter analysis.
Introduction
Have you ever seen the television show CSI? This show is about the exploits of a group of crime scene investigators who are interested in bringing criminals to justice by applying scientific principles. In real life, crime scene investigators are just as interested in making sure that justice prevails, and they are very meticulous. Every crime scene holds clues about what really occurred, and crime scene investigators have learned how to glean as much information as possible from a crime scene. Criminals unintentionally leave behind many clues about themselves at crime scenes. For example, they often leave footprints, hair samples, and evidence as to what kind of weapon they used to commit the crime.
Once the crime scene investigators gather all of the available evidence, they hand it over to the forensic scientists for analysis. The forensic scientists then use the evidence to reconstruct what occurred at the crime scene.
Forensic science includes many areas of study, such as criminalistics, engineering science, as well as pathology and biology. If a sports player were to die suddenly while playing a game, a forensic scientist with a specialty in pathology and biology would be called in to find out the cause. The scientist may have to perform an autopsy and examine the body to determine if the death was natural or not. A forensic engineer applies engineering principles to the purposes of law investigations. For example, engineers study failure analysis and evaluate the quality of construction and manufacturing of structures involved in a crime or catastrophic event. They may look into why a particular car rolled over or why a building or bridge collapsed. In general, to become a forensic scientist, you need to study math and science.
In this science fair project, you will become a crime scene investigator and a forensic scientist. In crime scenes where people are wounded, the investigators apply principles of blood spatter analysis. By taking measurements and observations of blood spatter, the investigators and forensic scientists can determine how the victim was hurt, what objects were used, and where in the area the wound was inflicted. Getting as much evidence as possible from a crime scene is important because it can mean the difference between stopping a criminal and letting that person go.
Figure 1. Forensic scientist determining point of convergence of blood shedding event.
Terms and Concepts
- Crime scene investigation
- Forensic science
- Criminalistics
- Pathology
- Blood spatter analysis
Questions
- What kind of evidence does a crime scene investigator collect at a crime scene?
- What is the difference between a crime scene investigator and a forensic scientist?
- What shape would a drop of blood have if it hit a wall at a right angle? What if it were traveling nearly parallel to the wall?
Bibliography
- 48 Hours, CBSNews.com. (2015, October 1). Science of blood splatter. Retrieved January 3, 2018.
- Layton, J. (2005, December 2). How Crime Scene Investigation Works. Retrieved December 8, 2008.
The following website is a bloodstain spatter analysis tutorial. There are some images of blood stains on this site. If you are squeamish, then do not look at this site.
- Forensicnursing.org. (n.d.). A Bloody Mess. Retrieved March 14, 2012.
If you need help understanding trigonometry, examine the the source listed below. You can also ask your math teacher for help and for more sources.
- Math is Fun. (n.d.). Introduction to Trigonometry. Retrieved May 17, 2023.
Materials and Equipment
For the Simulated Blood- Digital scale. A digital scale that would be suitable (the Fast Weigh MS-500-BLK Digital Pocket Scale) is available from Amazon.com.
- Cornstarch (44 grams [g])
- Container with lid, should hold about 2 cups of liquid
- Spoon
- Graduated cylinder, 250 mL; available from Amazon.com.
- Water (80 mL)
- Corn syrup (160 mL)
- Red food coloring (2-3 teaspoons [tsp.])
- Green food coloring (2-3 drops)
Note: All of the following items have the potential to get stained from the red food coloring, so be sure you are using disposable materials or have your parents' permission to use items that might get stained.
- Paper, 8.5 inches X 11 inches (1 ream)
- Scotch® tape
- Teaspoon
- Kitchen sponges (12)
- Latex gloves
- Clothes and shoes to wear that might get stained
- Goggles; available at your local hardware store
- Hammer
- Ruler with millimeter markings
- Adhesive circles; generally used to reinforce punch holes in paper and are available at office supply stores
- Kitchen string (1 roll)
- Protractor
- Scientific calculator
- Lab notebook
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Experimental Procedure
Making the Simulated Blood
- Using the digital scale, weigh 44 g of cornstarch and place it into the 2-cup container.
- Thoroughly mix 80 mL of water into the cornstarch with the spoon. The mixture must be smooth.
- Add 160 mL of corn syrup to the bowl and mix thoroughly. The mixture should be smooth.
- Mix in 2–3 tsp. of red food coloring. Stir until the mixture is a consistent color.
- Incorporate 2– drops of green food coloring.
- You should now have about 1 cup of simulated blood. Put the lid on the container and set the simulated blood aside.
Blood Spattering
- Find a location at your home or at school where you can conduct blood spatter experiments without making too much of a mess. Have all your supplies with you, including your lab notebook. Be sure to put on clothes and shoes that are okay to get stained. The location should be an interior corner so that you can capture the entire spatter. If you are looking at a corner and it looks like the letter "L," the interior is the inside of the L.
- Use the Scotch tape and the 8.5- X 11-inch paper to make two large sheets of paper, one for each wall. These large sheets of paper should fit onto as much of the walls of the corner that you found in step 1 as you or a helper can reach. Tape the large sheets into the corner.
- Tape down more paper to cover the ground in the corner so that you have a 3- X 3-foot area covered.
- Mark an "X" on the paper on the ground, about 58 mm from the corner.
-
Now, put on your latex gloves and add some of the simulated blood to one of the sponges, as follows.
- Use the teaspoon to add the simulated blood to the sponge, teaspoon by teaspoon, making sure not to soak the sponge. Keep track of how many teaspoons you add as you go along.
- The sponge should not be soaked or dry, but should be moist with the simulated blood.
- Record the number of teaspoons of simulated blood you used to moisten the sponge in your lab notebook.
- Place the edge of the moistened sponge at the "X."
- Put on your safety goggles. Hit the sponge sharply with the hammer. This should result in a spatter pattern on the paper. Remove the sponge and let the pattern completely dry. If you look closely at the simulated blood drops, you will see that they form ellipses. Crime scene investigators and forensic scientists can determine the position of the object that made the spatter pattern by taking measurements of the ellipses. They can determine the angle of impact of the drops. Knowing this and using string, they can then locate the position of the object in three dimensions. Observe the spatter. How far did the drops travel? What does the pattern look like? Do the ellipses end in tails? Record all observations in your lab notebook.
- Measure the angle of impact, θ, of the drops of simulated blood that made spatter marks on the walls, as follows. You will determine the angle of impact of just 5–6 spots on the walls. Mark the spots that you are measuring in order to keep track of them. Calculate the angle of impact for each spot using Equation 1, below. By measuring the length and width of the wide part of each spatter mark, you can determine the angle of impact. Record all data in your lab notebook. The angle θ is determined using the trigonometric function, arcsin or sin-1, as shown in Figure 2 and in Equation 1.
Diagram of a blood spatter on the ground leaves a distinct tail in the direction it was traveling. The blood drop has an outline similar to a ping-pong paddle where the handle will point in the direction of travel. When measuring the length of the droplet, investigators do not include the long end of the droplet.
Figure 2. This shows the length, a, and the width, c, of the blood spatter. This is the result of a drop of blood hitting the surface at an angle of impact, θ. The direction of the long axis shows the direction in which the drop was traveling when it hit the surface. Knowing the angle of impact and the traveling direction allow investigators to place the blood-shedding event in three dimensions.
Equation 1:
| Angle of impact = Arcsin ( |
|
) |
| θ = sin-1 | ( |
|
) |
|
- Now put yourself in the shoes of a forensic scientist. You appear on the scene and you see the blood spatters, but don't know the origin. Use a piece of kitchen string to determine the position of the sponge. Hold one end of the string in place, with an adhesive circle, at the first spatter mark you chose to measure . Sticking an adhesive circle to the paper around the blood spot will allow the blood spot to remain untouched if you need to make adjustments. Use the protractor and angle the string to the angle of impact that you calculated for the spatter mark, as follows. Make sure to line up the string along the long axis of the spatter (along the ellipse). The drop of simulated blood was traveling in the direction of the long axis as it turned into an ellipsis when it hit the paper. Place the protractor on the spatter mark, along the long axis, perpendicular to the paper. Hold the string along the protractor at the angle that you calculated for that spatter mark. This will take some time, so be patient. Hold the string taut and bring it all the way to the ground. Tape it to the ground with clear tape.
- Repeat step 9 for all of the spatter marks that you chose.
- Do the strings converge at the location where you hit the sponge? This is called the point of convergence or the origin. What is the difference in actual location and the calculated location?
- Repeat steps 2–11 at the same location, two additional times, with fresh materials. Record all of your observations and data in your lab notebook.
- Repeat steps 2–12 for two different locations on the paper in that same corner. For instance, try a location 51 mm away from the original location and then a location 100 mm away from the original location. Record all of your observations and data in your lab notebook.
Ask an Expert
Variations
- Experiment with the patterns that the simulated blood makes on different surfaces. If blood drops on a concrete surface compared to a tile surface, what is the difference in the resulting patterns?
- Confirm Equation 1. Using a burette stand, an eyedropper, and a clamp, drop simulated blood on angled cardstock. Does the impact angle of the drop correspond to the angle of the cardstock?
- When you aren't looking, have a volunteer hit the moistened sponge with the hammer, at a different location on the paper, and then remove the sponge. See if you can determine the location of the sponge using the angle of impact calculations.
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