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.
A. Preparation of “Exhibit A”
B. Preparation of “Exhibit B”
C. Preparation of “Exhibit C”:
D. Preparation of “Exhibit D”
E. Preparation of “Exhibit E”
F. Store the Evidence
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.
Modus Operandi (MO) sheets for each member of group, inkpad, FBI Fingerprint classifications.
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, 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.
Caution: Metallic dust can be harmful to the lungs if inhaled!!!!!
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.
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.
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!
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.
Exhibit C, iodine crystals in a screw-top jar, MO sheets, tweezers, roll of cellophane tape, plastic gloves.
Figure 3: The iodine vapor apparatus.
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.
Large jar, foil, “super-glue”, string, Exhibit D
Have students do the following:
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.
Exhibit E, magnifying glass, and MO sheets.
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