Fingerprinting analysis has been used for more than a century, yet it is still widely used in law enforcement agencies.  Because of its unique characteristic, it is conclusive evidence and a valuable tool among advanced technology even today.  However, there is a chance it might lose its ground by DNA fingerprint which is more sophisticated and accurate than traditional fingerprint.

There are three types of fingerprints that exist at crime scenes.  First, visible prints are made from finger stained with colored materials such as ink, blood, and grease.  In addition, plastic prints are formed by pressing onto a soft surface such as clay, soap, and wax.  At last, a latent print is an invisible print left on an object by the body’s natural greases and oils.  Because it cannot be seen by naked eyes, fingerprint powders, chemicals, and even lasers are used to make it visible on the crime scene evidence. 

The fingerprints can be categorized into three basic formations, which are loops, arches, and whorl.  Loops are lines that enter and exit on the same side of the print.  Arches are lines that start on one side of the print, rise into hills and then exit on the other side of the print.  Whorl is circles that do not exit on either side of the print.  The SENSE Holdings Inc. has a pretty good description regarding to types of fingerprints.  In addition, Dr. O’Connor’s Criminal Justice MegaLinks website covers fingerprinting procedures and technique in depth.

Following information are from Ward's Fingerprinting Analysis kit (36W5889) that was placed in order.  Do not duplicate or redistribute in any form unless you already owned or purchased this materials.

SIMPLIFIED FINGERPRINT ANALYSIS

WHY USE FINGERPRINTS IN A CRIMINAL INVESTIGATION?

According to most professional criminal investigators, fingerprints obey three fundamental principles. These principles are:

1. A fingerprint is an individual characteristic. It is yet to be found that prints taken from different individuals possess identical ridge characteristics.

2. A fingerprint will remain unchanged during an individual’s lifetime.

3. Fingerprints have general characteristic ridge patterns that permit them to be systematically classified.

The individuality of any fingerprint is based not upon the general shape or pattern that it forms, but instead upon its ridge structure and specific characteristics (also known as minutiae). The recognition of these ridges, their relative number, and the approximate location of them, on the observed print, are the special characteristics that make the fingerprint a specific identifying characteristic of each individual. There are at least 150 individual ridge characteristics on the average fingerprint. If between 10 and 16 specific points of reference for any two corresponding fingerprints identically compare, a match is assumed.

In a judicial proceeding, a point-by-point comparison must be graphically demonstrated for at least 12 different, but corresponding, points in order to prove the identity of a specific person. An example of typical ridge characteristics is shown in the drawing to the left.

IDENTIFICATION OF PRINT CHARACTERISTICS

There are three specific classes for all Fingerprints based upon their general visual Pattern. These are: loops, whorls, and arches. Approximately 60% of the total population have loops, 35% have whorls, and 5% have arches. The three major groups are also subcategorized based upon smaller differences existing between the patterns within the specific group. These subcategories are as follows:

Examples of each of these subcategories are illustrated as follows:

Of the two types of arches, the PLAIN ARCH is the simplest of all fingerprint patterns. It is formed by ridges entering from one side of the print and existing on the opposite side. These ridges tend to rise at the center of the pattern, forming a wavelike structure. The TENTED ARCH is similar, but instead of rising smoothly at the center, there is either a sharp up thrust or spike, or the ridges meet at an angle that is less than 90 degrees. Arches do not have type lines, deltas, or cores.

TYPE LINES are two diverging ridges usually coming into and splitting around an obstruction, such as a loop. A DELTA is the ridge point nearest the type line divergence. The CORE is the approximate center of the pattern. Examples of these characteristics are shown below:

A loop must have one or more ridges entering from one side of the print, recurving, and exiting from the same side. If a loop opens toward the little finger, it is called an ULNAR LOOP; if it opens toward the thumb, it is a RADIAL LOOP. The patterned area of any loop is surrounded by two TYPE LINES. All loops must have one delta. 

All whorl patterns must have type lines and a minimum of two deltas. A PLAIN WHORL and CENTRAL POCKET LOOP have at least one ridge that makes a complete circuit. This ridge may be in the form of a spiral, an oval, or any variant of a circular form. The main difference between these two patterns can be shown if an imaginary line is drawn between the two deltas contained within the two patterns. If the line touches any one of the spiral ridges, the pattern is determined to be a plain whorl, if no ridge is touched, the pattern is a central pocket loop. An example of this procedure is shown below:

The DOUBLE LOOP is made up of any two loops combined into one fingerprint. Any print classified as ACCIDENTAL either contains two or more patterns (not including the plain arch) or the pattern is not covered by other categories i.e., a combination loop and a plain whorl or a loop and tented arch.

Examples of these are more clearly shown below:

HOW PRINTS ARE USED IN A CRIMINAL INVESTIGATION

When the police or FBI book a person suspected of having committed a crime, the suspect’s fingerprints are taken and kept on file. These are DIRECT or INKED FINGERPRINTS which are the impressions of the ridge detail of the individual’s fingertips. About 200 million prints are on in the FBI Identification Division. Using modern computer technology, a set of prints can be run through scanning devices and matched with a possible suspect within minutes.

The term LATENT PRINT (hidden print) is a misnomer but often used inclusively. There are actually three kinds of CRIME-SCENE prints. These are:

1. VISIBLE PRINTS which are prints made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink.

2. PLASTIC PRINTS which are ridge impressions left on a soft material such as putty, wax, soap, or dust.

3. True LATENT PRINTS which are invisible print impressions caused by the perspiration on the ridges of one’s skin coming in contact with a surface and making an invisible impression on it. Perspiration contains water, salt, amino acids, or oils and easily allows impressions to be made.

The method used for obtaining latent prints depends on the type of surface to be examined, the manner in which the prints were left, and the quantity of material left behind. After the prints have been photographed, lifted and taken into the crime lab, they are then compared to the prints of all persons known to be at the scene of the crime or who had access to the crime scene. This procedure eliminates all but the criminal’s prints.

The most common techniques used to find latent or hidden fingerprints include:

1. Dusting with Carbon Powder on white or light colored surfaces.

2. Dusting with Lanconide Powder for black surfaces.

3. Dusting with Aluminum Powder for hard or dark colored surfaces as well as mirrors and metal surfaces.

4. Use of Cyanoacrylate (Super-glue) fuming.

5. Use of Iodine fuming techniques.

6. Use of ninhydrin.

7. Use of Silver Nitrate.

8. Use of Gentian violet.

9. Use of Laser technology.

Each group member will be responsible for preparing one set of three prints of evidence into a separate small baggie. The separate sets should then be placed into an evidence box for exchanging with another group at a later time.

Materials needed (per individual):

Microscope slide, 4 spoons, 24 1 1/2” x 1 1/2” squares of bond paper filter paper, and inkpad.

Procedure

A. Preparation of “Exhibit A”

1. Have students obtain a clean microscope slide. They should carefully handle it only be the edge. If it is not clean or print free, wash and rinse it with distilled water. Wipe it dry, making sure that no unwanted fingerprints appear on the glass surface.
2. Students will hold a microscope slide in a paper towel or cloth and place a distinct RIGHT thumbprint on the surface of the glass. If the print is smudged, is not clear, or is barely visible, wipe off the slide and try again. This time, have them rub their thumb over the oily portion of their face, blot the thumb, and then place a good print on the glass.
3. They then use a gummed label or grease pencil to label the slide “Exhibit A”.

B. Preparation of “Exhibit B”

1. Using a pencil, have them label a piece of filter paper “Exhibit B” at the top of the paper.
2. They then place a good, RIGHT thumbprint in the middle of the paper.

C. Preparation of “Exhibit C”:

1. Have students take a piece of bond paper and cut it up in 24 1 1/2” squares.
2. Using a pencil, have them label a piece of bond paper “Exhibit C” at the top of the paper.
3. They will then place good RIGHT thumbprint in the bottom 2/3 of the paper.

D. Preparation of “Exhibit D”

1. Have students obtain one spoon per group.
2. They will wash the spoon and rinse in distilled water. Wipe it dry, leaving no fingerprints on the surface.
3. Have them hold spoon in paper towel and place a right thumb print on the back of the spoon.
4. They then label spoon with a gummed label: “Exhibit D”.

E. Preparation of “Exhibit E”

1. Using a pencil, have them label a piece of bond paper “Exhibit E” at the top of the paper.
2. They will place their RIGHT thumb on the black inkpad and then place their thumbprint in the middle of paper. (They will share the inkpad provided.)

F. Store the Evidence

1. Using tweezers, have students transfer all the evidence to a box or tray and set aside until Part 3.

Preparation of direct prints for class file

Each student will fill out a Modus Operandi sheet using a fictitious name (Barb Wyre, Mike R. Fone, Polly Merz, etc.) but writing his/her real name on the back of the sheet. One person will act as the “officer on duty” and take the fingerprints of one of the other members of the group. Then students should change roles so that everyone’s prints will have been taken.

Materials needed

Modus Operandi (MO) sheets for each member of group, inkpad, FBI Fingerprint classifications.

Procedure

1. Make sure the inkpad had the proper amount of ink on it. Too much ink will produce unclear, smudge prints, too little ink will not allow the print to be transferred to the paper.
2. The “officer” takes the thumb of the right hand of the person and rolls it across the proper space on the MO sheet. This process is repeated for the remaining fingers on the right hand and then for the thumb and fingers on the left hand.
3. The “officer” dates and signs the MO sheets.
4. Soap, kitchen cleanser or similar product should be used to remove the ink from the skin.
5. Compare the prints with those on the FBI classifications. Under each print, write in the type of the print-loop, arch, etc. Are any of your prints exactly alike?
6. Place the MO sheets from all members of your group in the box containing the “evidence” prepared in Part 1.

Analysis of the “Evidence”

Each group should exchange their box of “evidence” and MO sheets with another group. Working together, students will analyze the fingerprints and determine the identity of the person who made them. For each piece of evidence, students should place the lifted print or the paper containing the developed print on the student data sheet and write down their final conclusions. Students should check the results with the other group and with the teacher at the conclusion of all lab work.

A. Dusting for and Lifting Prints from a Smooth, Non-porous Surface:

Exhibit A

Materials needed

Exhibit A, dusting brush, dusting powders (aluminum and carbon black), newspaper, cellophane tape, index card, magnifying glass, MO sheets.

This procedure should be done over a large sheet of paper or newspaper to facilitate clean up afterward.

Procedure

Students will:

1. Obtain a brush for dusting the print. Make sure it is clean and the bristles are separated from each other. Use a different brush for each powder.
2. Various dusting powders can be used depending on the type of surface to be examined. Use very fine carbon black powder on a white or transparent surface. Use a white powder like lanconide for prints on dark surfaces. Aluminum powder can be used on either type of surface. Use either the carbon black or aluminum powder to dust for the print on the slide.

Caution: Metallic dust can be harmful to the lungs if inhaled!!!!!

3. Take the carbon black and divide it up into 3 small beakers and label. Do the same with the aluminum powder. Each group will choose one the beakers. Dip the brush in the powder and lightly dust the area of Exhibit A containing the print.
4. Distribute the powder evenly over the surface that contains the print. If possible pick up the object that carries the print and tap the edge of the object to uniformly distribute the dusting powder.
5. After all of the print is developed remove the excess powder by blowing the dust from the surface or by gently brushing it away. Blowing the dust off the surface usually works better than the brushes supplied in the kit. If you do blow the dust off, be careful not to inhale any of the dust between attempts. If you elect to use the brush to remove excess powder, be careful not to destroy the print with too hard a brush stroke.
6. If a camera is available, try to photograph the print.
7. To lift the print from the slide to the index card, unroll about 5” to 6” of tape and place the end to the right of the thumbprint on the slide and allow the tape to cover to whole print. Slide a thumb over the tape and smooth it down over the print to force out air bubbles.
8. The print can be removed by puffing up on the roll end of the tape and then placing it on the fingerprint card in the same manner as the tape was placed over the latent print. Make sure the tape is secure. Cut the tape from the roll.
9. Everyone in the group should observe the print under the magnifying glass and compare it to the right thumbprints on the MO’s.  Identify the owner of the print and record this on the student data sheet.

B. Using Ninhydrin to Develop a Print of Paper

Ninhydrin reacts with the amino acids in the perspiration on the print to form a pink or purple compound. The reaction of ninhydrin with an amino acid is shown in Figure 2 on the next page. The blue colored substance (Ruhemann’s Purple) is formed by the reaction of some of the ninhydrin with it reduction product, hydrindantin, and ammonia.

Materials needed

Exhibit B, ninhydrin solution (prepared by adding the ninhydrin solid in the vial to the bottle of acetone), tweezers, plastic gloves, brush or cotton wads, MO sheets, and magnifying glass.

Procedure

Caution: Do the following in a fume hood or in a well-ventilated area. The acetone used in preparing the ninhydrin solution is volatile and flammable. Keep this solution away from open flames. Mix the ninhydrin and the acetone together. There will be enough for the four groups.

Note: Have students wear plastic gloves when working with the ninhydrin solution, as it will react with amino acids on your hands and turn them blue!

Students then:

1. Tape the top of Exhibit B to a paper towel.
2. Dip the tip of the brush into the ninhydrin solution and carefully dab this liquid over the fingerprint area. Do not use too much pressure since that will destroy the print. Cotton wads held with tweezers can also be used to dab the liquid onto the fingerprint area.
3. Allow the paper to dry. It may take 2-3 hours to develop. Tape the dry paper to the student data sheet. Observe the print under the magnifying glass and determine the identity of the person who left the print. Record your conclusion on the data sheet.

Note: If the print does not develop, expose the paper to the fumes from ammonia, i.e. by opening a bottle of concentrated ammonia in the fume hood and holding the paper with the print over the opening of the bottle. 

Figure 2: Ninhydrin Reaction Products

C. Using Iodine Crystals to Develop A Print on Paper

The dusting process used in Part A cannot be used to develop a print on paper, because the water from the perspiration spreads out and the print appears smeared. Exposing the print to iodine crystals will develop the print. The oily material on the print absorbs the iodine vapor and produces a violet to purple brown fingerprint.

Materials needed

Exhibit C, iodine crystals in a screw-top jar, MO sheets, tweezers, roll of cellophane tape, plastic gloves.

Procedure

Have students:

1. Wear plastic gloves to carry out the following steps.
2. Place about 2 grams of iodine in each of the six jars.
3. Cut a piece of tape about 1” long and place half of it on the top of Exhibit C. Open the jar containing the iodine crystals and quickly tape the paper to the lid so that the paper hangs down in the jar (See figure 3). Replace the lid and allow the print to come in contact with the iodine vapor for about 3 to 5 minutes or until the print is visible.
4. Once you can see the developed print, use tweezers to remove the paper from the jar. Be sure to quickly replace the lid on the jar.

Figure 3: The iodine vapor apparatus.

5. Observe the print under the magnifying glass. Determine the identity of the person who left the print and record your conclusion on the data sheet.
6. The developed print may disappear since the iodine will continue to sublimate. To “save” the print, completely immerse the paper in a solution containing 12.5 grams of calcium chloride and 43.9 grams of potassium bromide in l00ml of water. This will “fix” the print for a few weeks.

D. Using Cyanoacrylate to Visualize Prints (do one per lab group)

Caution: Super glue will adhere to your skin and possibly ruin the object being examined.

Materials needed

Large jar, foil, “super-glue”, string, Exhibit D

Procedure

Have students do the following:

1. Obtain a large container - e.g. large fruit jar.
2. Make a small aluminum bowl from the foil and center in the bottom of the jar.
3. Add 10-15 drops of super glue spread evenly across the bottom.
4. Suspend the spoon (Exhibit D) by a string into the jar. It should not touch the bottom or the sides of the jar. Cover the top of the jar tightly with foil and place a heavy object such as a book over the jar to make it airtight.
5. In 2 - 3 hours, a permanent print should appear.
6. Identify the print as before and record the results on the Student Data Sheet.

E. Identifying a Direct Print

Occasionally a criminal will leave behind a print that is clearly visible. Prints like these can be made by colored material that was on the person’s fingers. Substances that leave usable direct prints include soot, inks, blood, paints, facial make-up, and dyes. Usable direct prints can also be left on materials like window putty or clay that is soft enough to retain the image after the impression is made.

Materials needed

Exhibit E, magnifying glass, and MO sheets.

Procedure

Have students:

1. Use a magnifying glass to observe the inked print on Exhibit D. Compare this print to the one on the MO sheet.
2. Determine the identity of the print and record on the data sheet.

Final Analysis

Have them check their final results with their group, which prepared the “evidence” they, analyzed. Confirm their results with the classroom instructor.

Notes to the Instructor:

Additional information for future reference:
Searching for Clues James Sutton, 1997
DNA Fingerprinting C Lampton, 1991
‘Case Analysis Fingerprinting’, Laser, B.E. Dolrymple, Journal Forensic Science (586), 1979