Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Discreetly select two students from each class. Instruct them to follow the directions for Part A but have them place their fingerprints on the Evidence Fingerprint Card rather than a Suspect Fingerprint Card.
2. Make enough copies of the two Evidence Fingerprint Cards so each student will have an Evidence Fingerprint Record to use in Part B of this activity.

Safety Precautions

Isopropyl alcohol is a moderate fire risk as it is a flammable liquid. It is also slightly toxic by ingestion and inhalation. Wear chemical splash goggles. 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

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Used cotton balls and Fingerprint Records may be discarded in the regular trash according to Flinn Suggested Disposal Method #26a. Remaining isopropyl alcohol may be saved for future use or disposed of according to Flinn Suggested Disposal Method #18a.

Lab Hints

• Enough materials are provided in this kit for 30 students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period.
• Consider allowing the two students to bring the materials home to make the card. This will reduce the likelihood of the rest of the class figuring out the identity of the suspects.
• During Part B have students place their Suspect Fingerprint Cards around the room so that students can individually rotate to each station with their Evidence Fingerprint Records.
• Feel free to be creative when explaining the scenario of the suspect fingerprints to the students in Part B. One example being that fingerprints were taken off of a drawer which contained the answer key to an exam that has mysteriously gone missing.
• If you do not want to name specific students as the “criminals” you may assign each student a number to place on their fingerprint analysis sheet. Using this method, students can match the suspect number to the evidence as opposed to the name.
• Another option is to recruit two teachers to be the suspects. Have each complete an evidence card and suspect card. Collect all the suspect cards then substitute the two recruits’ cards for the similarly numbered student cards.

Sample Data

(Student answers will vary.)

Answers to Questions

1. Attach your suspect fingerprint record to this worksheet.

   Suspect Fingerprint Records must be attached.

2. Which two suspects matched the evidence provided from the crime scene?

   Verify students matched the correct suspect to the evidence card.

3. Tally the results of each fingerprint pattern in Table 1. Do the percentages of each pattern found in the class match the expected percentages found in the human population?

   The traditional values of each characteristic is loops 65%, whorls 30%, arches 5%.
   Sample Calculation: If loops are found in 18 of 30 students then 60% of the sample population has whorls, which is close to the expected 65%.

Teacher Handouts

10994_Teacher1.pdf

References

Federal Bureau of Investigation. Fingerprint Identification. http://www.fbi.gov/hq/cjisd/ident.pdf (accessed January 22, 2010).

Introduction

The fingerprint continues to be one of the most important and valuable pieces of forensic evidence. Fingerprints are unique for each person. There are even slight differences in the fingerprints of identical twins. By comparing fingerprints at a crime scene with a suspect’s fingerprint record, officials can establish a person’s presence at a particular location.

Concepts

• Forensics
• Ridge patterns
• Loops
• whorls
• arches

Background

Human skin represents the body’s first line of defense against foreign invasion and infection (see Figure 1). Skin is composed of an epidermal outer layer and a dermal inner layer. The surface between the epidermis and dermis is usually uneven, because the epidermis has ridges projecting inward and the dermis has finger-like papillae passing into the spaces between the ridges. This uneven boundary area is what contains the friction ridge structures responsible for our one-of-a-kind fingerprint patterns. These ridge patterns begin to form in the eighth gestational week and remain unchanged throughout an individual’s life. Typically, the only changes that occur thereafter are due to scar tissue.

Sweat glands are located in the dermis and their ducts extend up through the epidermis, where they release perspiration, oils and other materials through sweat pores. The perspiration, oils and salts from these sweat glands leave an identifiable residue conforming to the pattern of an individual’s fingerprints.

The human population has three main fingerprint patterns, each with various subgroups. A loop pattern has one or more ridges entering from one side, curving, and then leaving the same side it began, as illustrated in Figure 2—(1) Ridge Ending, (2) Bifurcation, (3) Enclosure, (4) Short Ridge, (5) Dot (Island). Loop patterns always develop ridges that diverge to form a delta. It resembles a “Y” pattern. All loops must have one delta.  A loop pattern on a fingerprint card that opens toward the thumb is a radial loop. A loop pattern that opens opposite the thumb is an ulnar loop, as shown in Figure 3. Remember, a fingerprint record is a mirror image of the actual fingerprint. Whorls are friction ridge patterns that have a minimum of two deltas as illustrated in Figure 4. There are four whorl subgroups: plain, central pocket, double loop and accidental. The plain whorl has two deltas and a complete ridge circuit. It is almost a “circular” pattern. The central pocket whorl differs from the plain whorl in one of the delta areas shown in Figure 4. The deltas are not symmetric and one side appears to be stretched like elastic (shown by the smaller circle).

The double loop whorl (see Figure 5) is composed of two loops and two deltas. The last whorl subgroup is the accidental (Figure 5). This pattern is defined as a “pattern consisting of a combination of two different types of patterns, with the exception of the plain arch with two or more deltas or a pattern which possesses some of the requirements for two or more different types or a pattern which conforms to none of the definitions.” Arches (see Figure 6) are friction ridges that enter on one side of the finger and cross to the other side rising upward in the middle. The simplest is the plain with mild bulging. The tented arch appears to have a spike acting as the pole in the middle. Fingerprints are processed through the Integrated Automated Fingerprint Identification System (IAFIS). The fingerprints are submitted electronically or by mail, processed by IAFIS, and a response is returned to the contributing agency within two hours or less for electronic criminal fingerprint submissions and 24 hours or less for electronic civil fingerprint submissions. Fingerprint processing has been greatly expedited with the implementation of IAFIS.

Experiment Overview

The purpose of this activity is to make a card with your fingerprints. Each class member will compare the fingerprints obtained for two individuals on the Evidence Fingerprint Record from a simulated crime scene to the fingerprints of up to 30 possible suspects in the classroom. Examine the evidence against each suspect to confirm the criminals’ identity.

Materials

Safety Precautions

Isopropyl alcohol is a moderate fire risk as it is a flammable liquid. It is also slightly toxic by ingestion and inhalation. Wear chemical splash goggles. If ink contacts clothing, rinse immediately to prevent the stain from setting. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Note: Obtaining clear, high-quality inked fingerprints takes practice. Pressing too hard or using too much ink may smear the fingerprint.

Part A. Ink Fingerprints

1. Wipe all 10 fingers using a cotton ball wet with isopropyl alcohol to remove excess oil.
2. Starting on the left side of your right index finger, gently and uniformly roll your finger to the right side of the ink pad.
3. Place the left side of your inked finger to the practice sheet.
4. Stabilize this finger by gently grasping with your left thumb and forefinger. Gently roll the inked finger to the right side while maintaining uniform pressure to avoid smearing.
5. Once the technique is mastered, repeat steps 2–4 to record your fingerprints on the Suspect Fingerprint Card.
6. Repeat this procedure for all fingers on the right hand.
7. Repeat the same procedure for all the fingers on your left hand, using a rolling motion from left to right. Use your right thumb and forefinger to guide your left fingers.
8. Set the Suspect Fingerprint Card aside and allow the ink to dry completely.
9. Wash your hands thoroughly with soap and water.

Part B. Fingerprint Analysis

10. Place your fingerprint card at a location in the room designated by your instructor.
11. Obtain a copy of the Evidence Fingerprint Record from your instructor.
12. Referring to the fingerprint patterns described in the Background section as a guide, identify the main patterns found in the suspects’ fingerprints. These patterns include loops, whorls and arches.
13. Note these key features with an arrow on the Evidence Fingerprint Record. Note: This will give a point of reference when comparing the evidence against all possible suspects.
14. Examine the right index fingerprint for each suspect. Identify which of the three main fingerprint patterns is present and record the patterns in Table 1 on the Fingerprint Analysis Worksheet.
15. Circulate through the room until the prints of all suspects have been examined and compared against the evidence.
16. Once Part B is complete, obtain your original Suspect Fingerprint Record and attach it to the Fingerprint Analysis Worksheet.

Student Worksheet PDF

10994_Student1.pdf