Introduction

Introduction

Fingerprints are very unique; the odds of having the exact same fingerprints as another person are about 1 in 10 billion on a planet with a population of roughly 7 billion people. Fingerprints are actually formed in the womb by the amniotic fluid swirling around the fingers of the fetus as they touch surrounding structures and are fully formed by the 17th week of pregnancy! Because of this fascinating and individual development process, fingerprints are very valuable evidence in a Forensic investigation. While identical twins may have the same DNA, they can always be differentiated by their fingerprints. A suspect may not see their fingerprints on a surface, but Forensic Investigators have several ways to make even the most elusive fingerprints reveal themselves!

Essential Questions

1. Why are fingerprints unique to each individual?

2. How are fingerprints classified and stored in AFIS?

3. How are fingerprints collected and stored?

Module Minute

Fingerprints are so unique that the odds of having the exact same fingerprints as another person exceed the population of our planet. Because of this uniqueness, fingerprints are routinely collected at crime scenes and stored in local, state and national databases for comparison. As technology continues to improve, the digital collection and collation of fingerprint databases is growing. While fingerprints can't be immediately and exactly matched by a computer as they are in popular crime television shows, they can be grouped by similarities and presented as possible matches for a fingerprint specialist to sift through. Fingerprints are most commonly collected from crime scenes by dusting and lifting with adhesive tape. Latent prints can be visualized with a number of processes such as Iodine or Cyanoacrylate fuming, Ninhydrin or Silver Nitrate applications.

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How Fingerprints are Formed

Introduction to Fingerprints

Dactylography, or the scientific study of fingerprints as a means of identification, is a very important part of Forensic Science. Fingerprints are one of the most reliable sources of individual evidence and they are a staple in most criminal cases when they are found in a crime scene. Fingerprints are a reproduction of friction skin ridges found on the palm side of fingers and thumbs. Friction skin ridges are also found on soles of feet and toes and can also be used to identify a person. Fingerprints are left behind due to sweat, oils, and dirt found on our hands. Fingerprints have been used for centuries to identify people and can be found on nearly every surface. This abundance of evidence littering the surface of so many objects is great news for investigators because fingerprints are considered individual evidence and may provide the key to solving a case.

Fingerprints are even more unique than DNA! No two people have ever been found to have the same fingerprints, whereas DNA can be shared between identical twins! Identical twins are produced from the same egg and sperm and therefore have identical DNA; fingerprints form separately on each twin as a result of amniotic fluid pressure on the developing skin. Additionally, fingerprints are often the way in which identical twins are differentiated in criminal cases. In July 2008, a woman was murdered in Georgia after a carjacking. The police found a cigarette at the crime scene with DNA matching a man identified as Donald Smith. When interrogated, Donald Smith denied that he had anything to do with the murder. When police showed him a video of the carjacking, Donald said that it was actually his identical twin brother Ronald. Authorities questioned his family and they also confirmed that the man in the video was Ronald. Police found a fingerprint in the car and were able to link it to Ronald. When confronted with DNA, video surveillance and a matching fingerprint, Ronald confessed to the crime. If a fingerprint had not been found, Donald could have been mistakenly convicted for a crime he did not commit!

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Classification of Fingerprints

Classification of Fingerprints

Three Fundamental Principles of Fingerprints

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

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 Processing

Fingerprint Identification Systems

Fingerprints are one of the best types of individual evidence because they are totally unique to each person. No two people have the exact same pattern of minutiae in their fingerprints, so it is very important that any fingerprints found at a crime scene are detected and analyzed! While a bloody patent print may be easy to see, latent prints can be quite difficult to find without special tools! Let's go over a few of the most common fingerprint detection and development techniques.

Latent Prints Methods

Powders - About 70% of fingerprint detection at crime scene is done using this method. Fingerprint powders come in a variety of colors but black is the most common for most light colored surfaces. On a darker surface, a lighter or fluorescent colored powder may be used for optimal detection. A fine brush is used to lightly dust an area with the fingerprint powder. Once on the surface, the powder reacts and sticks to any oils left behind. This method works best on hard, non-absorbent surfaces such as glass, tile, mirrors, and painted wood. Prints can then be "lifted" using clear tape. The developed print will be the same color as the applied powder

Cyanoacrylate Vapor - Commonly referred to as super glue fuming, this method is used on plastics, metals, glass, and skin (of cadavers). The object with the suspected fingerprint is placed into a fuming chamber with a small amount of cyanoacrylate. The cyanoacrylate is heated to release a vapor. The vapor adheres to the oil left behind by the fingers as they touched the object. Once dried, the print looks like a white or light colored three dimensional fingerprint on the object. This method is often successful when other attempts to obtain a latent print have been unsuccessful. The print is generally observable with the naked eye.

Ninhydrin - Ninhydrin is used to develop latent prints on paper, tissue or clothing. The object is sprayed, dipped, or "painted" with ninhydrin and left to dry for about 24 hours before the print can be visualized. The developed print will be purple due to a reaction of the Ninhydrin to amino acids and salts in the sweat and oil left behind on the paper. Once the Ninhydrin prints develop the characteristic purple color, they can be photographed for documentation.

Silver Nitrate - If a fingerprint is present on a wood or Styrofoam object, it can be visualized after it is sprayed with silver nitrate. When exposed to ultraviolet (UV) light, silver nitrate reacts with the salt in sweat to form a black/brown compound. The print will have a brown appearance when visualized under an ultraviolet (UV) light.

This type of fingerprint development is best used on porous surfaces, like paper or drywall.

Iodine Fuming - Iodine crystals are heated and through sublimation turn from solid to vapor (gas) without entering into a liquid phase. The vapor then adheres to the fingerprint and makes it visible in a characteristic brown colored print. This method will develop a latent print left on paper, cardboard, or an unpainted surface, however, the print will only be visible for a short period of time. When using this technique the print must be photographed as soon as possible.

Alternate Light Sources - Latent fingerprints can sometimes be located and visualized using alternate light sources such as UV light or special fluorescent lighting. Once they are visualized with the alternate lighting source, they are photographed and further processing such as dusting with fingerprint powder may then be completed.

Patent Print Methods

Photography - All patent prints are visible and are therefore photographed and documented visually as thoroughly as possible.

Amido Black - Bloody fingerprints found on a body are usually enhanced with Amido Black. This is a stain that reacts with any protein it encounters. Investigators use this stain to enhance bloody fingerprints on a body for better documentation and further analysis.

Plastic Print Methods

Photography - Because they are visible, plastic prints are generally photographed and collected for submission to the crime lab for further analysis when possible.

Fingerprint Analysis Process: ACE-V

Forensic Scientists follow a specific process in order to analyze fingerprints known as ACE-V. It is an acronym which represents the ordered steps in the process: Analysis, Comparison, Evaluation and Verification.

1) Analysis: The first step is to analyze the prints for comparison qualities. If a print is incomplete, too faint or does not display enough minutiae points to compare to another fingerprint, it is dismissed as unsuitable. If a fingerprint is found to be suitable for comparison to another fingerprint, it is documented with the most significant minutiae, as well as any scars or other markings which can help to identify the print. Whereas the Henry Classification System was once the main way in which fingerprints were differentiated for documentation, today they are are classified by pattern and minutiae points on each print within a massive fingerprint database maintained by the FBI known as IAFIS.

2) Comparison: A print from a person of interest, person from the crime scene or victim is compared to known prints to verify any matching sets. The examiner will look for matching minutiae points or other identifying characteristics. Matches can also be made through searching computer databases of fingerprints such as IAFIS.

3) Evaluation: This is the point in the process where the examiner decides if the prints match, do not match or are inconclusive. A print may be inconclusive for any of several reasons such as a poor quality print or an incomplete print without enough minutiae points.

4) Verification: In this step, the prints are evaluated by another examiner to verify the findings of the first examiner. If both concur, the prints are finished with the analysis process. If both examiners do not agree on the print, the process must be repeated or the fingerprint will be considered inconclusive and unusable.

An example of an exclusion; the print on the left does not match the known print on the right:

An example of how minutiae points are matched in a fingerprint during comparison and evaluation:

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IAFIS Database

Digital Imaging for Fingerprint Evidence

Integrated Automated Fingerprint Identification System (IAFIS): What is it?

 IAFIS is a national computerized system that allows fingerprints found at a crime scene or of a person of interest to be compared to a database of known fingerprints maintained by the FBI. In addition to fingerprints, the database also contains criminal history information about convicted persons, as well as mugshots, information about tattoos or distinguishing marks, physical characteristic such as height and weight, and aliases. It is one of the largest fingerprint databases in the world housing the prints and criminal history of 70 million convicted persons, as well as 34 million civilians! It also contains the prints and information (as it is available) of 73,000 known or suspected international terrorists! While that is a huge number of prints that the computer must sort when looking for matches, it generally takes less than an hour to get possible matches from the database. In fact, the average wait time is only about 27 minutes! 

How does IAFIS work?

Once a fingerprint is uploaded, the computer system will search for similar prints in the database. The computer will then print a list of close matches that a trained fingerprint examiner will use to ultimately determine a final match as outlined in the ACE-V Process. Before the IAFIS system, fingerprint examination was much more laborious and often took weeks or months to locate matching fingerprints in older paper-based systems. While today's system does not have instantaneous results as you may see on television, it is certainly a vast improvement over previous methods!

Did you know that fingerprints collected at a police station or for civilian purposes such as pre-employment background checks are now usually scanned directly into a computer rather than using the ink and card method of the past? These new fingerprint capture devices often use a liquid such as water on a scanner screen to create a print that is scanned. The prints can then be printed on a standard fingerprint card and submitted for the intended purpose as well as directly uploaded to IAFIS. This is a vast improvement because the finger can be scanned repeatedly as needed until an acceptable, very clear fingerprint is captured.

 Georgia Virtual, Fingerprints, CC BY-NC-SA 3.0