Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Select a male student from the class to serve as the guilty party. Note: Instruct the student when working with his lab group that the group should take an impression of his foot.
2. Have this student make an impression of his shoe in the BioFoam^®. The specific instructions may be found in steps 3 and 4 of the Procedure section.
3. Cast the impression using calcium sulfate and water so it will be ready to be analyzed with the other evidence on Day 2 of the laboratory activity.
4. Once the cast has dried and been removed from the foam, label it as “Evidence.”
5. On Day 2, set each of the eight footwear impressions and the evidence impression around the classroom with numbers corresponding to each suspect on the list. If you wish you may also write the suspect’s name on them.
6. The selected male student performing the Prelab Preparation’s footprint should match suspect 7—Kyle Long.

Safety Precautions

The BioFoam^® contains ≤ 1% formaldehyde. It causes skin and serious eye irritation. It may cause an allergic skin reaction and cancer. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Lab Hints

• Enough materials are provided in this kit for 8 groups of students. This laboratory activity requires two class periods. In the first class the impression and casting may be performed. In the second class the worksheet questions can be answered using data from the samples.
• If possible conduct the Prelab Preparation a day or two before the lab is performed in class. This will give the selected guilty party the opportunity to wear a different pair of shoes for each casting so the answer isn’t glaringly obvious on Day 2 of the activity.
• Make sure the student group impressions correlate with the suspect list. For example, four of the student groups should cast a female’s footwear impression and the other four groups should cast a male’s footwear impression.
• This activity was tested mixing calcium sulfate hemihydrate with tap water. However, depending on your water quality, it may be necessary to use distilled or deionized water.
• If desired, the footprint may match a suspect other than Kyle Long.

Teacher Tips

• Enhance the story by allowing students to perform the other lab kits in the Flinn Forensic Files Series:
  • FB2094, Flinn Forensic Files—Fingerprint Exploration
  • AP7745, Flinn Forensic Files—Ink Inspection
  • FB2096, Flinn Forensic Files—Finding Evidence in Fibers
  • AP7050, Flinn Forensic Files­—Ballistics

Answers to Prelab Questions

1. Why are footprints present at almost every crime scene?

   A person committing a crime must, in some way or another, enter and exit the crime scene. This is most often done on foot, even if only for a short distance, making footwear prints available at almost any crime scene.

2. What challenges do you envision detectives experiencing when attempting to take footwear impressions at actual crime scenes?

   The medium that the footwear print is in can present additional challenges. For example, snow is not as easy to cast as mud. Also, weather conditions can alter the prints. If it has rained heavily since the print was made it may not be usable at all.

Sample Data

Answers to Questions

1. Based on recent suspects and arrests of other crimes in the area, police have taken the impression of eight different suspects for this crime at Ms. Combs’ house. Measure the length of each of the eight suspects shoe casts and record in the table above.

   See the Sample Data table.

2. Based on the analysis of the evidence, which suspect appears to have the same size shoe as the sample evidence from the crime scene?

   The evidence shoe footwear impression should be the same length as Kyle Long. Note: Additional suspects may also match the length depending on the size of classmates’ shoes.

3. Sometimes more than one suspect is possible based on the footwear analysis, what other tests could be done to determine the guilty party?

   Investigators could also search the crime scene for fingerprints, hair and fiber analysis and DNA to further determine the guilty party.

References

Hilderbrand, D. S. Footwear, The Missed Evidence. http://www.crime-scene-investigator.net/footwear.html (Accessed July 2018).

Introduction

Tracks left by footwear are a valuable piece of evidence at crime scenes that is often overlooked. Learn the different ways that tracks from shoes can be used to develop possible suspects in a criminal case.

Concepts

• Forensics
• Footprint impressions/casting

Background

The Case

Alyson Marie Combs had just flown back to her Columbia, SC home after vacationing in Kennebunkport, ME. Her summer vacation was cut short after learning that $20,000 was missing from her checking account. After speaking with her personal banker, she flew home to determine what had happened. When she entered her home everything seemed fine. Once she entered her home office in the back of the house she discovered the window had been broken. Ms. Combs’s home has a heavily wooded yard making breaking in from the back of the house easy to disguise. The first thing Alyson did was open the desk drawer where she normally keeps her checkbook and found it was missing. She called the police immediately. While they were unable to find much evidence, they did find a footprint outside the window in the dirt. Police took photographs and impressions back to the lab for the case file.

Technical Aspects

Footwear impressions are often used to place a suspect at a crime scene. It makes sense that a criminal must enter and exit the crime scene on foot at least for a short distance, making the footprint a common denominator in most crime scenes. Criminals have realized it is important to conceal their fingerprints with gloves or their faces with masks. In fact, in the wintertime you might not think anything of a person wearing either of those accessories. However, most people don’t wear shoe covers in their daily lives and doing so would cause a person to stand out.

Footwear evidence is obtained by prints or impressions. Just like fingerprints, footwear prints can be visible or latent. Visible prints are found when the footwear is contaminated by a foreign object such as blood or wet paint. The person then steps on a clean surface leaving a visible print. Latent footprints are commonly overlooked as they are not visible unless they are dusted with powder just like fingerprints. Footwear evidence can also be obtained by taking impressions. Impressions are taken when the footprint is evident on a softer surface such as wet sand, mud or snow. First, the medium is treated with a hardening spray followed by casting similar to that used to take dental impressions. Once the casting material has hardened, the 3-D model can be compared to suspects’ footwear as well as saved with other evidence for future reference.

Experiment Overview

In this experiment, the casting of one group member’s shoe will be made. This casting will be treated as the evidence from the crime scene to answer all post-lab questions.

Materials

Prelab Questions

1. Why are footprints present at almost every crime scene?
2. What challenges do you envision detectives experiencing when attempting to take footwear impressions at actual crime scenes?

Safety Precautions

The BioFoam contains ≤ 1% formaldehyde. It causes skin and serious eye irritation. It may cause an allergic skin reaction and cancer. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Making the Impression (Day 1)

1. Obtain a box of footwear foam and open it carefully. Note: Touching the foam with your fingers, even lightly, will leave an impression.
2. Select a group member to make a footwear impression.
3. Step gently onto the foam, depressing your shoe about half-way through the foam. Do not place too much weight on the impression foam.
4. Carefully remove your shoe from the foam. Another group member may need to hold the box down so the impression is not damaged by wiggling your foot to remove it.
5. Very lightly sprinkle talc powder over the impression to serve as a fixative. Tap the sides of the box over a garbage can so that that talc is evenly distributed over the impression.

6. Measure 425 g of calcium sulfate in a 1-gallon resealable bag.
7. Measure 215 mL of distilled water and add it to the plastic bag containing the calcium sulfate.
8. Seal the bag making sure it is completely closed.
9. Shake the bag vigorously for 30 seconds.
10. Gently knead the contents of the bag for 1–2 minutes. Verify that the contents of the bag are not lumpy and are roughly the consistency of pancake batter. If not, add 10 mL more water at a time until desired consistency is achieved.
11.  Open the top corner of the bag and gently pour it at an angle into the foam casting. Do not pour directly on the casting where the flow of the material will change the cast.
12. Allow the casting to harden for 30 minutes or until hard to the touch.
13. Remove the casting and foam from the box.
14. Gently peel away the layers of foam from the casting. Note: As the foam is removed, check that the casting has properly solidified before vigorously removing excess foam.
15. Once the impression has completely hardened, clean off the excess foam by brushing the impression with a beaker brush to remove foam from the smaller grooves of the impression.
16. Turn the casting in to your instructor.

17. The eight suspects’ footwear impressions have been placed throughout the laboratory as well as the evidence impression from the crime scene. Measure the length, in cm, of each impression as well as record any observations that distinguish the footprint such as type of tread or brand of footwear.
18. Complete the Flinn Forensic Files—Footwear Evidence Worksheet once all data have been gathered.

Student Worksheet PDF

12497_Student1.pdf