Fundamental Principles of Fingerprints

Question

1. A fingerprint is an individual characteristic; no two fingerprints have been found to have identical ridge characteristics. This means that even identical twins have different fingerprints!
2. Fingerprints remain unchanged during an individual's lifetime. Injuries such as superficial burns, abrasions, or cuts will not affect the print pattern or alter the dermal papillae. The original pattern will always be duplicated whenever any new skin grows back.
3. Fingerprints have general ridge patterns that permit them to be systematically classified.
Common Types of Fingerprints
There are 3 main patterns of fingerprints; Loop, Whorl and Arch. Some patterns result in a combination of 2 or more of these patterns; these are called "composite patterns". See below for characteristics of fingerprint pattern types.
Characteristics of Fingerprint Pattern Types

Pattern Name
Description
What % of the population has at least one?
Types
# of deltas
Loop


Ridge lines enter and exit from the same side of the finger.


60-65%
Ulnar Loop: Loop opens toward little finger.

Radial Loop: Loop opens toward thumb.

All loops have ONE (1) delta.
Whorl

Whorls have one ridge line that makes a complete circle around the finger. Also, they have 2 deltas.
30-35%
Plain Whorl: Simplest and most common whorl. One complete circuit with spiral or circular shape.

Central Pocket Whorl:Same as plain whorl, but one of the lines curves around a second time.

Double Loop: Two loops combine to make a whorl pattern. It is often also considered a composite pattern. It must have 2 deltas to be considered a type of whorl.

All whorls have TWO (2) deltas.
Arch

A pattern where the ridge lines enter from one side and leave on the opposite side in the shape of an arch. The lines of the pattern lie one on top of the other forming the "arch".
5%
Plain Arch: Wave-like pattern where the line enters on one side of the finger, rises subtly in the center like an ocean wave and exits on the other side of the finger.

Tented Arch: Arch pattern with sharp spike at the center of the wave pattern. The spike is shaped like a tent; thus the name!
No deltas or cores.


*It is important to note that when making determinations of pattern with Radial and Ulnar Loops, it depends on the hand from which the print came from! The names "Radial" and "Ulnar" refer to the Radius and Ulna bones of the forearm and the direction that the loops face in correlation with those bones. The Radius bone will always be on the "thumb" side of the arm and the Ulna will always be on the little finger side of the arm. Because of this, the loops will face different directions toward little finger and thumb on each hand. See the images below of various fingerprint patterns for a visual representation of how this applies to fingerprints!

When describing fingerprint patterns, it is important to understand a few basic terms.
Minutiae - Also known as ridge characteristics; minutiae are major features or details of a fingerprint. These details enable examiners to make comparisons of one print with another. Some minutiae found in fingerprints include: bifurcation, core, delta, or island. Minutiae are specifically what make fingerprints individual evidence! Everyone has patterns of loops, whorls or arches in their fingerprints, but the types and placement of minutiae are unique in each person's fingerprints. Typically, 8-16 minutiae point matches identified by a forensic fingerprint expert in a fingerprint is considered a positive match if (and only if) there are NO non-matching minutiae points present! If an additional minutiae point is present in one print that is clearly absent in the other, this automatically becomes a non-match or an exclusion.
Delta - A delta is a minutia pattern within a fingerprint that resembles the Greek letter delta, Δ, and is the result of two diverging lines with the pattern. The two deltas in this whorl pattern have been circled in red.

Core - Center area of a fingerprint. In a whorl, it is the center of the spiral. In a loop, it is a top part of the innermost loop. The core of this Loop fingerprint has been circled.

Types of Fingerprints
Fingerprints can be left on nearly every solid surface; some are easily spotted while others must be coated with powder or viewed under special lighting in order to be seen. A Forensic Scientist has several techniques that can be used to both spot and preserve the three types of fingerprints found in a crime scene. The three types of fingerprints are:
Patent - Fingerprints made after ridges come in contact with a colored material such as blood, dirt, paint or ink. The print is transferred to a surface using the colored material as the "ink". These types of prints are also called visible prints.

Plastic - Fingerprints that are left on a soft material such as soap, clay, wax, or paint. The print is generally three dimensional and remains visible within the soft medium.

Latent (invisible) - Fingerprints are left on a surface as a transfer of body oils and sweat to the surface of an object. They aren't usually seen without the aid of fingerprint powder, reagents or special lighting.

Fingerprint Discussion
A man walked into Smallville Apartments and burglarized several units. When the Smallville crime scene investigators arrived, they found two fingerprints on the counter in one of the units that they believed were left by the perpetrator. The first fingerprint was classified as a loop and the second fingerprint was classified as a whorl. The investigators went back to the police station and looked through their fingerprint cards until they found a local man with a record of driving while under the influence of alcohol who had both loop and whorl fingerprint patterns on the same hand. They arrested the man confident they had found the perpetrator.

ANSWER the following question in the text box and turn in a picture of your drawing:
Why are they wrong to be confident in their arrest and what errors in investigating fingerprints did they make? You should discuss at least three reasons the investigators are incorrect in this situation.
What type of prints were collected from the kitchen counter, patent, plastic, or latent?
Construct an explanation for what technique could be used to lift and evaluate these prints.

Answer 1

The investigators in the Smallville Apartments case are incorrect to be confident in their arrest for several reasons:

1. Lack of Individualization: Just because the suspect has both loop and whorl patterns does not provide sufficient evidence to conclude that the prints found at the scene belong to him. Fingerprint analysis relies on minutiae points, which are the unique ridge characteristics that differentiate one fingerprint from another. The investigators did not confirm that there were enough matching minutiae points between the collected prints and the suspect's fingerprints to establish a definitive match. Without a minimum of 8-16 points being verified and no non-matching points being present, they cannot claim with certainty that the fingerprints belong to him.

2. Insufficient Comparison Process: The investigators rushed to identify the suspect based solely on the observation that he had similar types of prints (loops and whorls) without thoroughly comparing the specific patterns and minutiae of the collected prints to those in the suspect’s record. A detailed side-by-side comparison is necessary to substantiate any match or exclusion based on specific details of ridge endings, bifurcations, and other minutiae.

3. Ignoring Other Possibilities: Fingerprints can be found at a crime scene that do not necessarily belong to the perpetrator. The area might contain prints from previous occupants, visitors, or maintenance staff. The investigators did not consider the likelihood that the prints belonged to someone else who had legitimate access to the apartment. A proper investigation would require a wider range of fingerprint analysis and consideration of the circumstances surrounding the scene.

Regarding the type of prints found on the kitchen counter, it is likely that they were latent prints. These are invisible to the naked eye because they are left by the transfer of body oils and sweat when a person touches a surface.

To lift and evaluate the latent prints, the investigators could use fingerprint powder as a lifting technique. Fingerprint powder comes in various colors and is chosen based on the contrast with the surface where the print is located. The investigators would lightly dust the surface with the powder using a soft brush to adhere to the oils in the latent prints. After the latent prints are made visible, they can then use clear adhesive tape to lift the prints from the surface for further examination and analysis in the lab. This method allows for better preservation and clarity of the prints to compare against known samples.