Teacher Notes

Flinn Forensics Files—Fingerprint Exploration

Student Laboratory Kit

Materials Included In Kit

Isopropyl alcohol, 28%, 250 mL
Complete Suspects Fingerprint Record Sheet
Cotton balls, 50
Fingerprint Record Cards, 30
Index Fingerprint Cards, 35
Ink pads, 8

Additional Materials Required

Copy machine*
Soap and water
*for Prelab Preparation

Prelab Preparation

After Part A has been completed all students will have provided their Index Fingerprint Card. Ten of these fingerprints will be used as the prints of the suspects from the crime scene.

  1. Randomly select one of the Index Fingerprint Cards. Make enough copies of that one fingerprint for everyone in the class. This will be the evidence fingerprint which was taken from the dresser.
  2. Once copies have been made attach the same fingerprint used in step one on the appropriate location for Kyle Long on the Complete Suspects Fingerprint Record Sheet. Note: Kyle Long will be the guilty party who stole the passports. If you wish to not name a student as the guilty party (Kyle Long) you may choose to use your own fingerprint for steps 1 and 2.
  3. Randomly select nine other Index Fingerprint Cards. Place a card next to the name of a suspect on the Complete Suspects Fingerprint Record Sheet.
  4. Repeat step three with the remaining eight cards. Note: You do not need to keep track of which student was placed with a given suspect as these prints will not match anything from the crime scene.
  5. Once completed, make enough copies of the Complete Suspects Fingerprint Record Sheet for everyone in the class.

Safety Precautions

Isopropyl alcohol is a flammable liquid and vapor. It causes serious eye and mild skin irritation. May cause drowsiness or dizziness. Use in well-ventilated area. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.


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 sheets 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 working individually. This lab is best performed over two lab periods, although it might not consume the entire time. There should be a break between Parts A and B so the instructor can make copies of the Complete Suspects Fingerprint Record and the Index Fingerprint Card of the two “suspects.”
  • It is recommended not to distribute the copy of the crime scene Evidence Fingerprint until after step 3 in Part B is completed. Otherwise students may be tempted to visually match the print without analyzing the fingerprint pattern components.
  • If desired, have students go back to their fingerprint Record Cards and count the number of loops, whorls and arches of their own fingers. Compile the entire classroom's data if time permits.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Developing and using models
Analyzing and interpreting data
Obtaining, evaluation, and communicating information

Disciplinary Core Ideas

MS-LS1.A: Structure and Function
HS-LS1.A: Structure and Function

Crosscutting Concepts

Structure and function

Performance Expectations

MS-LS1-1: Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells
MS-LS1-3: Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.
HS-LS1-2: Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

Sample Data

Student answers will vary.

Answers to Questions

  1. Attach your Fingerprint Card to this worksheet.

    Fingerprint card must be attached.

  2. Which suspect matched the evidence provided from the crime scene?

    Kyle Long

  3. Tally the results of each fingerprint pattern in the data table. Do the percentages of each pattern found in the suspects match the expected percentages found in the human population?

    The traditional values of each characteristic are loops 65%, whorls 30%, arches 5%.
    Sample Calculation: If loops are found in 6 of 10 suspects then 60% of the sample population has whorls, which is close to the expected 65%.

Teacher Handouts



Federal Bureau of Investigation. Fingerprint Identification. http://www.fbi.gov/about-us/cjis/fingerprints_biometrics/fingerprint-overview (accessed April 11, 2014).

Student Pages

Flinn Forensic Files—Fingerprint Exploration


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.


  • Forensics
  • Ridge patterns
  • Loops
  • whorls
  • arches


Case Background

James and Carly Frank live in Newberry, SC. They recently decided they wanted to replace their ceramic tile kitchen floor with hardwood. They met with Damon Hinger from DreamSteps flooring. Although his product was impeccable, the price was a bit high. The following day the Franks met with Sylvia Sauk from Forever Floors. They decided to go with Forever Floors as the quote was more reasonable and they offered a quality product. Before materials could be ordered Kevin Cook from Forever Floors needed to come to the Frank’s home to measure the room. However, the cost to remove the current ceramic was quite expensive through the flooring company. The Franks decided to check the classified ads in the paper to see if anyone was looking for work doing manual labor. They were intrigued when they found an ad for a young man named Kyle Long with five years of construction experience. The Franks called Long and they agreed to meet to set up an estimate. As luck would have it, Long’s quote came in at about half of what the flooring company was going to charge. They told him that he had a deal and he could start the next morning. After Kyle left, Carly mentioned she had noticed that he had an uncanny resemblance to her husband James.

Long spent the next week breaking and ripping up the tile floor while Carly was home doing chores. Carly worked as a school teacher and was off for summer break. After Long was done, the Franks paid him and he went on his way. The next day Tim Sauder, Jose Santos, and Jeff White who work for the flooring company, installed the hardwood floors in the kitchen. The Franks were happy with their work as their kitchen is finally what they had envisioned.

Two weeks later the Franks were packing for their upcoming vacation to Aruba and Carly noticed that she could not find their passports. James said “aren’t they always in the top left dresser drawer?” Carly replied “yes, they are always there but they aren’t there anymore.” The Franks were now in quite the pickle as their vacation was two weeks away and their passports were nowhere to be found. They knew the passports had not been misplaced as they were always extremely diligent about never keeping them anywhere else. The Franks called the police and explained their passports were missing. Since they had several contractors in the house over the past month the police thought it would be a good idea to take some fingerprints near the dresser.

They began analyzing the evidence by ruling out any prints obtained from the dresser that matched James and Carly. The next step was to compare the prints lifted from the dresser to those prints obtained from anyone who had done work in the Frank’s home. James and Carly prepared a list which consisted of Damon Hinger, Sylvia Sauk, Kevin Cook, Tim Sauder, Jose Santos, Jeff White, and Kyle Long. Carly also reminded James that two months ago they had the carpets cleaned by Comfort Cleaners who sent Alicia Sorrentino, Midge Hart and Brett Phelps to do the job. Since Carly was not 100% certain she had seen the passports since the carpet cleaners left they were added to the suspects list as well.

Technical 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.

{11241_Background_Figure_1_Human skin cross section}
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 in which (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.
{11241_Background_Figure_2_Loop pattern with ridge characteristics}
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.
{11241_Background_Figure_3_Ulnar and radial loop patterns on a left hand}
Whorls are friction ridge patterns that have a minimum of two deltas as illustrated in Figure 4. There are four whorl sub-groups: plain, central pocket, double loop and accidental.
{11241_Background_Figure_4_Plain and central pocket whorl patterns}
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 sub-group 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.”
{11241_Background_Figure_5_Double loop and accidental whorl patterns}
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.
{11241_Background_Figure_6_Arch patterns}
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 in 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

Practice comparing fingerprint patterns, like those used in the crime scene, in your own lab. On day one, each student will take their fingerprints and submit a copy of their right index finger to the instructor. These will serve as the evidence of fingerprints gathered from a crime scene. On day two, you will be given a copy of a suspect's fingerprint to determine if there is a match to the fingerprint found at the crime scene.


Isopropyl alcohol, 28%, < 1 mL
Complete Suspects Fingerprint Record Sheet
Cotton ball
Crime Scene Evidence Print
Fingerprint Record Card
Index Fingerprint Card, 2" x 1½"
Ink pad (shared)
Practice paper
Soap and water

Safety Precautions

Isopropyl alcohol is a flammable liquid and vapor. It causes serious eye and mild skin irritation. May cause drowsiness or dizziness. Use in well-ventilated area. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.


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 Fingerprint Record Card.
  6. Repeat this procedure for all other fingers on your 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 Fingerprint Record Card aside and allow the ink to dry completely.
  9. Complete your Index Fingerprint Card by making a print of your right index finger. Give the card, with your name on the back to your instructor.
  10. Wash your hands thoroughly with soap and water.
Part B. Ink Fingerprints
  1. Obtain a copy of the Complete Suspects Fingerprint Record Sheet from your instructor.
  2. Referring to the fingerprint patterns described in the Background section as a guide, identify the main patterns found in the Compete Suspects Fingerprint Record Sheet. These patterns include loops, whorls and arches.
  3. Note these key features with an arrow on the Complete Suspect Fingerprint Record. Record the number of each feature found per suspect on the Flinn Forensic Files—Fingerprint Exploration worksheet.
  4. Compare the Crime Scene Evidence Print to each of the prints on the Complete Suspect Fingerprint Record identifying whorls, loops, and arches.
  5. Complete the Flinn Forensic Files— Fingerprint Exploration Worksheet.

Student Worksheet PDF


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