It is easy to make a blood spatter lab for your students! With just a little prep, and some fake blood, your kids can experience blood evidence for themselves!
My favorite forensics topic is Blood Spatter evidence. Every year, I am newly amazed by how much can be learned and deduced from blood spatter at a crime scene. It is a subject that students really have no pre-understanding of. I love seeing the surprise on their faces as they learn more and more about what blood spatter can tell us.
What Blood Spatter Tells Us
First, we can learn blood type from drops found at a scene. Blood type can help determine who left the blood behind. Does the blood type match the victim? If not, we are looking for a suspect with that particular blood type. A great example is the Jeffery McDonald murder case: every member of the family had a different blood type!
But blood spatter can teach us much more than just blood type! Of course we can get DNA from blood (which I defer to when we are in our DNA Evidence Unit!). We can learn…
- If the assailant was right or left handed
- Roughly how many blows a victim received
- The type/size of weapon used in the attack
- Where the victim and assalant were in the room for each blow
- The direction and speed of movement for victim and/or assailant
Wow!! No other type of evidence can tell us so much!
Make a Blood Spatter Lab
In my Forensics Class, I first introduce and define the three basic types of blood spatter: Low Velocity, Medium Velocity (including cast off and blunt force spatter) and High Velocity. I do not go into a lot of detail about what the spatter can indicate, but just enough so that students have something to ‘hang’ their learning on during the lab. Here are the notes I give!
To really gain an understanding of how blood spatter works, my students complete a Blood Spatter Lab. I love this lab!
It is designed to let students experiment with the different Low and Medium Velocity blood spatter patterns that can be generated in various crime scene scenarios. We then use what they have learned through experience, and their own pictures, to go into detail about spatter at a crime scene.
Here are the materials we use:
- Fake blood – There are a lot of recipes out there, but I have found that watered down red (washable!) paint works the best. I mix it at about a 1:3 ratio of paint to water, or until the consistency is just thicker than water, so it makes a nice spatter pattern when dropped.
- Dropper bottles (or containers and pipettes)
- Paper to spatter on – I collect scrap paper all year for this activity!
- Clipboards or something to hold paper at an angle
- Large pieces of paper or cardboard for blunt force spatter and cast off spatter- this was the trickiest part for me. I used three cheap tri fold poster boards and had students clip on their own pieces of bulletin board paper
- Washcloths or sponges to soak with ‘blood’
- Hard surface outside
- A variety of small and large weapons: plastic knife, baseball bats, long wood board, screwdriver, hammer, etc. I brought some from home and had students bring some
Mimicking Blood Spatter Patterns
The idea is to experience all of the spatter patterns that may be found at a crime scene. Some are not possible to replicate (gunshot spatter comes to mind!) but most are!
Drops from Heights
Have your students drop blood from varying heights off the floor or table. Notice the spatter spreads out further, with more satellites, the higher up you go. Also experiment with multiple drops on top of one another (making a pool of blood) from different heights! Note what happens the further the drop falls.
Drops At Different Speeds
When blood falls straight down, the drop is round. But when it falls with forward momentum, because it is dripping from a person while running, the drop will be elongated. Give students a long piece of poster paper, laid on the ground or on desks. Holding a full dropper, students will walk and drip blood onto the paper. Then have them run while dripping blood. Notice the pattern difference! How can the shape of the blood drop reveal the direction the person was moving?
Hitting the Wall at an Angle
When a drop hits the wall, the angle/direction it came from can be determined with a simple calculation. By calculating the angle and direction of multiple drops, investigators can figure out a location in 3D space that the blood came from – the location a victim was in the room when the assault happened. At this point in our learning, I want students to see how drops hitting at different angles result in different shapes. The smaller the angle, the longer the drop!
Give students scrap paper (I save all of my misprints from the whole year!) clipped to a clipboard. Using a protractor, they can change the angle of the clipboard in relation to a drop of blood from above. When the board is flat on the table, the drop hits at 90 degrees and is round. Lift the board off the table at 45 degrees and the drop will look elongated. A 20 degree angle (from the dropper) will have a very long extended shape.
This demonstration will lay a strong foundation for students when we begin learning how to calculate the angle of impact and determining the point of origin later in the unit!
Impact Spatter Patterns
Soak a sponge or washcloth in the blood substitute. Place it on a hard surface outside – blood will go everywhere! Students hit the sponge with a bat, pole, hammer, or some other heavy blunt object. To catch the spatter for observation, set up a piece of poster paper just in front of the sponge. The first few years, I had one student hold the paper while a partner would hit the sponge. This led to a lot of complaints about bloody shoes/shirts/arms! So now I use a few dollar store trifold cardboard poster boards and binder clips to attach poster paper. If it is a windy day, the poster boards can be leaned against an outside wall. As long as you are using washable materials for blood, it will not be a problem if the building gets a bit messy.
TIP I learned the hard way: don’t let students put the soaked sponge on the sidewalk/pavement directly – it will crack under the force of a high school student swinging his hardest! Put the blood soaked sponge on a wood board or brick/paver, and set up in the grass!
Cast Off Spatter Patterns
Provide both small and large ‘weapons’ for students to choose from: a plastic knife, baseball bats, long wood board, screwdriver, hammer, scissors, etc. I bring some things from home and have students bring some. They will need at least one large and one small ‘weapon’ in order to compare the cast off patterns.
Provide another large piece of poster paper to capture the pattern. Like the impact spatter, this exercise is best done outside, using a trifold poster board to hold the paper.
Students can dip the weapon in blood, or use their dropper to put a generous amount on the end of the weapon. Have them slowly raise the weapon, and swing down quickly towards the poster paper. Repeat this with the same weapon, but starting low and swinging quickly upwards. Blood will fly off the weapon, leaving elongated drops revealing the direction of travel. Large weapons will leave larger drops, while cast off from small weapons leaves small drops.
Classroom Management for the Blood Spatter Lab
Students do best (and learn most) working in pairs (or groups of three if you are low on materials). Each part of the lab is set up in stations, which pairs are free to move to and from as they need, and as stations open up. Some stations take more time (castoff and impact spatter) so I have more availability at those locations – enough materials for five pairs at a time. Other stations (running vs walking drops) can be done quickly, so only two pairs can be doing that at once.
I wanted the Lab to be digital so students could post their own pictures to it, and then use the photos for reference when we discussed the spatter patterns in detail. Photos of student work are also so much easier to grade – no worry about letting the spatter patterns dry somewhere and collecting huge stacks of paper from each student!
I created a Google Doc Lab template with instructions, questions to answer, and locations for students to embed photos of their blood spatter within the digital lab sheet. Pairs get their own digital copy of the Lab sheet to complete.
I give my students one day to make all the drops and collect photos of their work. They get time the next day to load photos on the Lab document and answer the questions. We have 80 minute block classes.
Save your time and get this lab from our store ready to use! It comes with a full key (including photos!) and video instructions showing how to do each part of the activity.
Students love this lab! It is so much fun to really get into the blood spatter, and really helps them understand what can be a complicated subject.
As an extension, if time allows, students do a mini-research project on a famous case involving blood spatter. Ranker has a great list of summaries, thirteen cases that students can dig deeper into and learn about spatter evidence used in real life. Sometimes they present the cases to the class, while other times I allow them to rotate around the room sharing what they learned with just a few people at a time.
What is your favorite Forensics topic to teach? Share with us in the comments below!