Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Make 15 copies of the Fingerprint Record Sheet. Cut in half along the dashed line.
2. Cut the sheets of black and white paper into half. Cut each half into thirds. Each pair of students should use one black ⅙ sheet and one white ⅙ sheet.
3. Cut the Crime Scene Fingerprints into 24 separate squares.

Safety Precautions

Charcoal powder is flammable. Please review current Safety Data Sheets for additional safety, handling and disposal information before beginning this activity. Remind students to wash their hands thoroughly after completing this activity.

Disposal

The black dusting powder and the white dusting powder may be disposed on in the regular trash or kept for future use.

Teacher Tips

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory can reasonably be completed in one 50-minute class period. The Prelab Questions may be completed before coming to lab.

• Students may begin this activity station lab at any particular activity. In order to complete the entire activity within one 50-minute period, students must rotate every eight minutes. This will allow five minutes to begin and conclude the lab period as an entire class.
• The classifications in Activity A are subject to some debate since entire prints are not always visible. Encourage discussion of the discrepancies. The prints can also be further classified into subgroups in some cases.
• Have plenty of cleanup materials available when conducting this laboratory. Have plenty of soap, water, scrub brushes and paper towels.
• Enlist the “secret” help of a student and have them leave fingerprints of various fingers on glass slides just before class. Then have students lift the latent prints and try to track down the suspect by examining all of the class fingerprint records.
• Use fingerprint records from multiple classes to create even more difficult mysteries or combine fingerprinting with other forensic activities for a more in-depth mystery.
• Mark half of the brushes for use with dark powder and the other half for use with white powder to avoid contamination between brushes.
• A comprehensive forensic timeline is available at www.forensicdna.com.
• This activity is a perfect opportunity to involve your local law enforcement officials. Invite police/forensic officers to address your class. They love to visit classes. They will explain how new technology has nearly eliminated the “ink-type” fingerprinting process. Computer scanned fingerprints are more accurate and make retrieval and identification significantly faster.
• Latent prints can be “lifted” chemically and these techniques are of great interest to forensic scientists. Most require chemical procedures too dangerous for most classroom use.

Answers to Prelab Questions

1. Create a pie chart representing the proportion of each fingerprint pattern found in the human population.

2. What is the preliminary classification for a person with a whorl on both the right ring and the left ring fingers?

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Answers to Questions

Activity A. Fingerprint Classification

Fingerprint A: Loop
Fingerprint B: Loop/whorl
Fingerprint C: Whorl
Fingerprint D: Whorl
Fingerprint E: Loop
Fingerprint F: Loop
Fingerprint G: Loop
Fingerprint H: Loop 
Fingerprint I: Arch/loop
Fingerprint J: Loop
Fingerprint K: Loop
Fingerprint L: Whorl
Fingerprint M: Whorl
Fingerprint N: Arch
Fingerprint O: Arch
Fingerprint P: Loop
Fingerprint Q: Whorl
Fingerprint R: Whorl

Note: Student answers may vary slightly since the fingerprint edges are often cut off.

Activity B. Matching Fingerprints

Activity C. Classifying Your Fingerprints

1. Compare your numbers to others in your class. Does anyone else have the same numbers? Explain why or why not.

Student answers will vary.

2. Are any of your ten fingers identical? How does your left hand compare to your right hand? Explain.

Each finger may or may not have a whorl for each individual. The print on any one finger will different somewhat from any other finger’s print.

Teacher Handouts

10191_Teacher1.pdf

References

Clark, S.; Quigley, M. N.; Tezak, J. J. Chem. Ed., 1993, 70, 7, 594–595.

Kimbrough, D. R.; DeLorenzo, R. J. Chem. Ed., 1988, 65, 10, 1300–1301.

Schiltz, G. Forensic Laboratory Science and Detective Mystery Writing; Flinn Scientific, Inc., Batavia, IL, 1994.

Siegal, J. A. Forensic Science—The Basics; Taylor & Francis, New York, 2007.

Introduction

The fingerprint is still one of the most important and useful pieces of forensic evidence. No two persons’ fingerprints are alike, not even identical twins. This uniqueness allows fingerprints to continue to be strong evidence for identification of individuals at crime scenes.

Concepts

• Ridge patterns

• Loops
• Whorls
• Arches
• Fingerprint classifications

Background

What Is a Fingerprint?

Human skin (see Figure 1) represents the body’s first line of defense against foreign invasion and infection. 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 the individual’s life.

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, oil and salts from these sweat glands leave an identifiable residue conforming to the pattern of an individual’s fingerprints.

Fingerprint Patterns

There are three main fingerprint patterns, each having various subgroups, found in the human population:

These three main categories were first published in a book titled Finger Prints by a nephew of Charles Darwin. Sir Francis Galton’s book, published in 1892, served as a foundation upon which modern fingerprint techniques are based.

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. 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 as 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 while rising upward in the middle. The simplest is the plain arch with mild bulging. The tented arch appears to have a spike acting as a pole in the middle.

Individual Ridge Characteristics

There are five ridge characteristics: bifurcation, short ridge, enclosure, dot (or island) and ridge ending as shown in Figure 7.

Fingerprint Classification

Fingerprints are analyzed and classified a number of different ways to expedite retrieval and identification. The recognition of the ridges, their relative number, and approximate location are key to identifying the print with the individual. There are at least 150 individual ridge characteristics on the average fingerprint. The greater the number of identical matching points on a fingerprint the greater the chances of the match. In a judicial proceeding a point-by-point comparison is usually made graphically to convince the jury of a match.

A preliminary classification method, which is only a very small part of the FBI classification method, is based upon whorl patterns of all ten fingers. The classification begins by identifying the presence of any whorl patterns. Whorl patterns are assigned a numerical value based on the finger on which the whorl is found. The formula and values are outlined in Figure 8.

The values for the top row are added and become the numerator. The values of the bottom row are added and become the denominator. The results are express as a fraction.

The preliminary classification for an individual with only one whorl, which is on his right index finger would be:

This preliminary classification is just one of many sorting methods used by FBI computers to narrow the number of possible matches to suspects. New computer scanning techniques will rapidly be replacing these older classification methods.

Experiment Overview

The purpose of this “activity-station lab” is to investigate fingerprint patterns and fingerprinting techniques used as part of a forensic investigation.

Materials

Prelab Questions

Read the Background section thoroughly prior to answering the following questions.

1. Create a pie chart representing the proportion of each fingerprint pattern found in the human population.
2. What is the preliminary classification for a person with a whorl on both the right ring and the left ring fingers?

Safety Precautions

Do not do this activity in the presence of other chemicals. Charcoal powder is flammable. Wash hands thoroughly after performing this activity.

Procedure

Activity A. Fingerprint Classification

1. Use the Primary Classification Worksheet to record your classification of each fingerprint from A through R.
2. Do not write on the Fingerprint Card Set. Classify each print as loop, whorl or arch. Use as many subcategories as possible. Refer to the Background section as needed.

Activity B. Matching Crime Scene Fingerprints

1. Determine if there is a match between any of the known suspects and prints on the Fingerprint Card Set.
2. Find at least one individual ridge characteristic that clearly matches the suspect to the crime scene print.
3. Record your findings on the Primary Classification Worksheet. Record your suspect’s fingerprint number and defend your choice.

Activity C. Inked Fingerprints

Making good, clear inked fingerprints requires practice and deliberate work. Pressing too hard or using too much ink may smear the fingerprint. Practice on scratch paper before making your actual print record.

1. Starting on the left side of your right index finger, gently and uniformly roll your finger to the right side of the ink pad.
2. On scratch paper, place the left side of your inked finger down.
3. Grasp this finger with your left thumb and forefinger and gently roll to the right side while maintaining uniform pressure to the finger to avoid smearing.
4. Repeat this procedure for your right hand fingers until your print is of acceptable quality for fingerprinting on the Fingerprint Record Sheet.
5. Fingerprint the fingers on your right hand on the Fingerprint Record Sheet.
6. Repeat the same procedure for the fingers on your left hand with a rolling motion from left to right. Use your right thumb and forefinger to guide each finger during the process. Remember to maintain uniform pressure to the fingers to avoid smearing.
7. Set the Fingerprint Record Sheet aside to let the ink dry completely.
8. Wash your hands thoroughly with soap and water.
9. Refer to the Fingerprint Background Information and do a preliminary FBI number classification for your personal finger-prints. Record your results on the Primary Classification Worksheet.

Activity D. Latent Fingerprints on a Non-Porous Black Surface

1. Find a clean area on a black lab table and gently press your thumb down on the table edge to leave your thumb print. Hint: If necessary, run your fingers through your hair several times to increase the amount of oil on your fingers in order to leave a latent print.
2. Use the brush to gently “float” a small amount of white dusting powder onto the latent print area. Be sure to add the powder very slowly—until you can see the print clearly. Do not add so much powder that you fill in the space between the ridges.
3. Once the print is visible, gently brush in the direction of the friction ridges to avoid smearing.
4. Obtain about 3 inches of lifting tape. Adhere the tape to the base of the print (edge of table). Holding the tape taut and beginning at the base of the print, gently begin pressing down the tape as it moves upward and beyond the print. Try to avoid air bubbles and smearing.
5. Gently pull back the tape, lift the print, and place the print on one half of the piece of black paper. Label the print with your name. Your partner should do the same with the other half of the paper.
6. Wipe the table with a damp cloth.

Activity E. Latent Fingerprints on a Non-Porous Surface

1. On a clean, dry glass slide, gently press your thumb down leaving a fingerprint. Hint: If necessary, run your fingers through your hair several times to increase the amount of oil on your fingers in order to leave a latent print.
2. Use the camel hair brush to gently “float” a small amount of black dusting powder onto the latent print area. Be sure to add the powder very slowly—until the print is clearly visible.
3. Once the print is visible, gently brush in the direction of the friction ridges to avoid smearing.
4. Obtain about 3 inches of lifting tape.
5. Adhere the tape to the base of the print. Holding the tape taut, gently begin pressing down the tape moving upward until the tape is adhered beyond the top edge of the print. Note: Avoid creating air bubbles and smearing. If a mistake is made, begin again.
6. Gently lift the tape and print from the glass slide. Place the print on one half of the piece of white paper. Label the print with your name. Your partner should do the same with the other half of the paper.
7. Wash the glass slide with soap and water. Carefully dry the glass slide with lens paper. Wipe the table with a damp cloth.
8. Wash all surfaces with soap and water. Most of the ink used for fingerprints will wash off initially with soap and water. Minute traces of ink remaining will be gone in a day or so.

Student Worksheet PDF

10191_Student1.pdf