Forensics Crime Lab
Grade level(s):Grade 5, Grade 6, Grade 7
Subjects(s):Biology/Life Science, Chemistry, Science Skills
How can we us evidence to investigate a crime scene?
Forensics, Circumstantial evidence, Blood Type, Coagulation, Antigen, Antibody, Microscope objective, Microscope Lens, Chromatography, Solvent, Dissolve
What you need:
Part One: Crime Scene & Evidence Collection:
All of the followinng items are available at the Resource Center, Kit #K255. If you do not have access to the Resource Center, please assemble the following:
-Yellow caution tape
-Five red fabric items
-5 black felt tip markers
-Large zip-loc bags
-slides with fabric samples (available in Kit #K255)
- "Blood" (1 cup milk + red, green, & blue food coloring)
- Small tubes or small plastic cups
- Small bottles, with vinegar or water
-Five black felt tip markers collected from each of the suspects. (Labeled 1 - 5).
- paper towels or coffee filters cut in rectangles
- Pencils and tape
- Container (e.g. beakers, tupperware)
There are many ways to group students. Observation of the crime scene can be done together as a class. In the second part of the lesson, three groups for the evidence analysis (blood typing, microscopy, and chromatography) work well.
A large classroom
This lesson can be done in two parts or as one long lesson.
Part One: Crime scene discovery introduction. ~ 1 hour.
Part Two - Process the evidence. ~2 hours, including review, stations, and wrap-up. Each group spent about 15-20 minutes at each station.
A crime is staged in the classroom. After observing the crime scene, student identify and collect crime scene evidence. Students use blood typing analysis, microscopy, and chromatography to analyze the evidence. The list of suspects is narrowed to identify the potential culprit. This lesson may be done in two parts or as one long session.
How to use a light microscope
1. Brainstorm different ways to look for evidence and investigate suspects
2. Use microscopes to compare and contrast threads collected at the crime scene to threads collected from clothing of the five suspects
3. Understand the principles of blood typing and coagulation
4. Perform paper chromatography to analyze the ink extracted from the ransom note to ink taken from the suspects' pens
5. Record observations, sketches and results in their official "Investigative Report.doc"
6. Will discuss circumstantial evidence and use the process of elimination to identify a perpetrator
Blood typing (See attachment "BloodTyping Background.doc")
Chromatography (See attachment "Chromatography Background.doc")
Materials Needed (detailed explanation):
Part One: Crime Scene & Evidence Collection:
-Ransom note on paper towel (Write a ransom note according to the "crime" committed in the classroom.)
-If 5 adults are available, the adults can be labelled as "Suspects."
Kit #K255 at Daly Ralston Resource Center contains all other crime scene and suspect evidence.
If you do not have access to the Resource Center, you need to prepare the following materials:
-Yellow caution tape to "secure the crime scene"
-Five red fabric items (e.g. sweater, tie, bandana, scarf, hat etc)
-5 black felt tip markers (e.g. 3 Sharpie Industrial Strength, 1 Sharpie Permanent and 1 water soluble Sharpie).
-Tweezers for collecting threads of fabric
-Ziploc bags for collecting threads and the ransom note from the crime scene
-Five plastic bags for gathering evidence from suspects
Preparing for Part One: Crime Scene & Evidence Collection
A crime scene must be set up in the classroom during a time when the students are not around. Secure the crime scene with yellow caution tape to prevent students from readily accessing it. Plant evidence consisting of blood, red threads and a ransom note within the crime scene area.
Part Two: Evidence Analysis
-microscopes (light or dissecting) or magiscopes or hand lenses
-seven glass slides of fabric samples - one for each suspect and two evidence slides
-1 cup blood (for evidence and blood samples): 1 cup milk + 10 drops red food coloring + 1 drop blue + 1 drop green (adjust as needed)
-small tubes or small plastic cups (e.g. salad dressing cups)
-pipettes or droppers
-Five vials or cups containing "blood" from each of the suspects and the crime scene.
-A box containing a bottle of "antiserum A" and and a bottle of "antiserum B" for each suspect. (**See attached document "Suspect.xls"). These bottles will either be water or vinegar depending on the desired outcome of typing each suspect. **It's criitical that these bottles are prepared for each suspect and kept separately.
Paper Chromatography (see diagrams)
-Five black felt tip markers collected from each of the suspects. (Labeled 1 - 5).
-paper towels or coffee filters cut in rectangles.
-Pencils and tape
-Chromatography Container (e.g. beakers, deep tupperware container).
-Rubbing alcohol (Isopropanol)
Preparing for Part Two: Evidence Analysis
Blood Typing: Assemble six boxes (one for each suspect, one for evidence collected at crime scene), each containing 1 plastic disposable pipette, 2 small clear plastic tubes (such as ml eppendorf tubes), vial of 'blood' (milk with red, green and blue food coloring added), "anti serum A" and "antiserum B"
[NOTE: the anti serums in each box will either be vinegar or water, and what is in each bottle will determine the blood type that the students conclude they have found. Therefore it is very important that each suspect have their own Antiserum A and Antiserum B and that the bottles not be exchanged between suspect boxes. Please see " Suspect.xls" attached to this lesson for instructions on setting up the antiserum. *** Also, fresh pipettes and tubes will have to be placed in the boxes after every group has used them].
Microscopy: Set up several microscopes
Paper Chromatography: A solution of ink from the ransom note needs to be prepared prior to the lesson. It is possible to extract the ink from the ransom note with isopropanol; however, this isopropanol solution of ransom note ink is significantly more dilute than the ink contained in the suspects' markers. Thus, it can be difficult for the students to match the ransom note ink with any of the markers. This can be solved by concentrating the ink extracted from the ransom note to a minimal amount of solvent. Alternatively, you can remove the ink cartridge from the marker and dissolve some directly into isopropanol.
Lesson Implementation / Outline
To begin, the kids entered the classroom and discovered the crime scene. Let the kids get excited and observe the scene without disturbing it (Caution tape wrapped around the scene). The teacher then explains that he/she came back to find this crime committed and called in forensic scientists to help the students solve the crime. Students then sat down and we began a brainstorming session. What evidence could they see? What might we collect and how might we evaluate it? What other evidence may we look for (ie look for witnesses)? Why is it important to collect evidence very carefully?
1. Preparation. The correct markers and red clothing items are distributed to the suspects according to the lesson table. (Suspect 3 is the culprit) One or more suspects may wear discreetly placed Band-Aids indicating they may have cut themselves recently. (Note: Our lesson included theft of the class lizards. The Band-Aids suggested that the perpetrator may have been bitten by the lizards during the theft) Stage the crime scene by placing drops of 'blood' near some sharp object, red threads that may have been torn on some surface and a ransom note written with a black sharpie-type marker in the area. Secure the crime scene using the yellow caution tape.
2. Arrival of student - Introduction and brainstorming session (see questions asked above). Get witness to implicate five different individuals seen in the area.
3. Evidence collection - Allow students to examine the crime scene. What evidence do they see? We allowed one student to enter the crime scene for up close inspection. Demonstrate collection of evidence to minimize contamination/mishandling. Seal evidence in Zip-Loc bags.
4. Suspect questioning - Break the class into three groups (predetermined by teacher if possible, with numbers or colored dots written on student nametags). Each adult/teacher leads a group to collect evidence from one or two suspects. Note that if not enough adults are available, a teacher (or a" policeman") can present the evidence. In each group, put one student in charge of plastic bag for collecting evidence from each suspect (marker & red clothing item). Evidence should be clearly marked as belonging to 'Suspect 1' through 'Suspect 5'. Students and/or scientist then demands that the suspects go to school nurse to give a 'blood sample'. Students may also ask if the suspects have an alibi for the approximate time of the crime.
5. Wrap up - Students return to classroom with the labeled bags of evidence. Teacher lead a brainstorming session. What kind of experiments can we do with the evidence we collected?
1. Introduction and Recap - Remind students what was collected yesterday & review the evidence. Generally explain the basic ideas behind each experiment. Hand out a summary sheet (see attached "Official Crime Scene Investigative Report") for recording data from the three experiments. Break students back up into their three groups. Each adult/teacher will be in charge of one group and lead them to the experimental station.
2. Forensic experiments:
a. Blood Typing. Prior to student arrival, assemble six boxes: one for each of the suspects, and one belonging to the 'evidence' collected at the scene. Each box should contain: 1 plastic disposable pipette, 2 small clear plastic tubes (I used 1.5 ml eppendorfs), vial of 'blood' (milk with red, green and blue food coloring added), and "anti serum A" and "antiserum B" [NOTE: the anti serums in each box will either be vinegar or water, and what is in each bottle will determine the blood type that the students conclude they have found. Therefore it is very important that each suspect have their own Antiserum A and Antiserum B and that the bottles not be exchanged between suspect boxes. Also, fresh pipettes and eppendorfs will have to be placed in the boxes after every group has used them]. Do not distribute these boxes until right before it is time to do the experiment or the kids will just play with them. Use whiteboard or posters to explain concepts of blood typing and coagulation. Show drawing of red blood cells with different antigens on the surface and how this is what differentiates A, B, AB and O type bloods. Explain that we are going to determine the blood type of our suspect. Go over the exact steps thoroughly:
1. Use pipette to fill eppendorf ~ halfway with suspects blood.
2. Add 4-5 drops of "antiserum A". Cap tube and invert multiple times. Do you see coagulation? Record.
3. Repeat with fresh tube and Antiserum B. Record data. What is your blood type?
Note: Vinegar should cause noticeable "coagulation" of milk.
Distribute boxes to kids, ideally having one or two kids in charge of one suspect. After all students have typed their suspect, have students compile data on the table in their handout "Investigative Report." Who can they eliminate?
b. Fabric Analysis
Gather clothing evidence and prepare slides (or prepare them in advance) containing a thread or a few threads from an article of clothing that was worn by the suspect or found at the scene of the crime. Suspects may want to have an alibi as to how the tear in the fabric was made if it is detected by observant students. Set-up light microscopes around a table or on a counter against a wall, each with a different sample or evidence slide.
Observation: The students should draw, in the appropriate circles on their "Investigative Report," what they see under the microscope for each of the suspect and evidence slides. Students must be instructed to note the texture, thickness, color hue, and should note any variations in color or subtle patterns in the fiber itself. Students should draw their fibers big enough to show detail instead of drawing a number of uninformative scribbles. If possible, students should go back and compare the evidence slide to suspect fibers they think are most similar. Students must be careful to around the microscope or else they'll accidentally bring it out of focus, requiring their own intervention to regain focus or the intervention of a teacher or assistant.
In our class, there was a general consensus among the different groups of kids as to which suspect or suspects most closely had a red fabric fiber that matched the evidence.
c. Chromatography of ink in Ransom Note
At the Chromatography station, have students gather around the table. Review vocabulary words such as chromatography and solvent. Explain that paper chromatography can be used to separate the components in ink. We will compare the ink from the 5 suspects' pens to the ink from the ransom note. Ask the students to open their "Investigative Report" to the section on paper chromatography. Using the picture as a guide, go over how they will prepare their own chromatography paper.
You can make the ransom note with a paper towel (see "Chromatography set-up" diagram). Cut strips from the ransom note for comparison or make an extraction of the ink from the note by dissolving it in isopropanol and then concentrating the solution.
Prepare paper towels for the chromatography by cutting pieces that fit on the containers for the chromatography. Before giving students their materials, take a pencil and show how to mark the paper with pencil. Make pencil dots for markers 1 - 5. Have the students label each dot (as shown in their worksheet). Each of the suspects' pens should be labeled 1 - 5. Demonstrate for the students how to take a marker and make a small dot on each of their pencil marks. Pass out paper towel and pencils to the students.
The "Crime Scene Investigative Report" will allow students to record what they are seeing and understanding. Also, frequent 1-on-1 interactions are helpful to assess student understanding and provide additional explanation as needed.
Subgroup conferencing - As the final activity reaches an end, have each group go over the evidence they have collected and discuss who they think is the culprit.
Summary/Review - Have students return to their seats in the classroom. On the classroom board, make a table with the following columns: Evidence and Suspect 1, 2, 3, etc, in rows, and Blood Type, Ink Analysis, Fabric Analysis, and Circumstantial evidence (See "Suspect.xls" as a guide). Ask students what suspects' evidence matched the evidence found at the crime scene. Ask students who they think is guilty, and why. Have students raise hands and answer questions individually. What experiment was the most conclusive? What other questions might be asked? What other experiments would give helpful information?
Ending - Students may either conduct a class trial, or the culprit may be confronted with the evidence and plead guilty.
Optional: The class may also conduct a "trial" with the top three suspects.
Extensions and Reflections
Conduct a trial with the top three most likely suspect. Evidence may be tampered with to make the conclusion less decisive. This will help student understand the legal process and ideas such as 'innocent until provent guilty', 'tampering with evidence' 'circumstantial evidence' etc.
If other adults are available during the lesson to act as suspects, prior to the lesson, evidence can be distributed to the suspects. The students then can collect the evidence from the suspects.
If you have access to TLC (Thin Layer Chromatography) plates and equpment, the students may use TLC chromatography instead of paper chromatography. The principles are exactly the same; the main difference is that a silica gel is used instead of paper to separate the components of the ink.(Seee "investigative Report with TLC.doc".)
****There are many different ways this lesson can be done and many different types of evidence that can be collected, including handwriting analysis, hair analysis, fingerprinting analysis. These extensions will be added to the lesson in the future
|Investigative Report .doc||49.5 KB|
|BloodTyping Background.doc||88 KB|
|Chromatography set-up.doc||35 KB|
|Investigative Report with TLC.doc||52 KB|