Fingerprint Analysis

Analyzing fingerprints left at the scene of a crime is one of the most critical parts of a forensic analysis. Fingerprint analysis typically helps to connect the crime to a person who may have been present at the scene but csn also be used to track a person’s previous records; arrests, parole, and other details.

Forensic fingerprint analysis has been used to identify criminals for more than one hundred years. The process begins with a deposited, or “latent,” print found at the scene of the crime. If the print is detailed enough, fingerprint analysts visually compare the latent print from the crime scene to the fingerprint of a suspect. Analysts compare qualities such as the general shape of the prints, the shape and depth of the ridges in the print, and the length of each ridge. The analyst then relies on his or her experience to make an evaluation of the prints, either to identify a match or exclusion. Another analyst then verifies the first analyst’s conclusions; through this process, a suspect is determined to have deposited the latent print or not.

About Fingerprint Analysis

It is often said that no two people’s fingerprints are exactly alike, and that therefore a latent print found at the scene of a crime which matches the suspect’s prints has to mean the suspect left the print at some point in the past. This assertion, however, is not based on any studies, research, or analysis. In other words, there is no scientific basis for the belief that fingerprints are unique to each person. In fact, a high profile innocence case shows how wrong this assertion is. In 2004, Brandon Mayfield, an attorney from Oregon, was arrested as a material witness by the FBI because his fingerprint matched a latent found at the scene of the Madrid train bombings. The bombings killed 191 people and injured hundreds more. Mayfield was held for 17 days before Spanish authorities conducted their own analysis and found the real culprit: an Algerian national, Ouhnane Daoud, who along with others orchestrated the terrorist attack. The FBI later apologized to Mayfield and conducted an extensive review of their fingerprint analysis procedures.

The main problem with fingerprint analysis is one consistent with many other areas of forensic science: subjectivity. Instead of relying on tested scientific methods, the process is mostly based on the subjective beliefs of the analyst. The process is intentionally kept subjective so the examiner can consider the quality of each individual ridge in the particular prints being examined, but that leads to unreliable results that are generally not repeatable. The features compared in each fingerprint analysis are not predetermined for their reliability; rather, they are chosen by the examiner at the time of the analysis based on which features are of the highest quality.

Despite this subjectivity, fingerprint analysts also typically testify in terms of absolute certainty. However, because of the lack of validity of the testing and retesting process, the lack of standards used for determining a match or exclusion, and the overall subjectivity of the process indicates that the analyst is not truly absolutely certain of anything – except the fact that he or she truly believes a match exists – results tend to be misrepresented to juries as scientific certainties. The National Academy of Sciences opines that while fingerprint analysis likely can be a useful tool in the courtroom, to claim that it has no error rate is simply wrong. The Academy has called for continuing research so that “examiners could begin to attach confidence limits to conclusions about whether a print is linked to a particular person.”

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Principles behind fingerprint analysis

The furrows and ridges present on your fingers, toes and palms create a unique pattern. Fingerprint analysis relies on this unique pattern, and forensic scientists will group patterns into the following  distinct groups:

Loops: This pattern recurves on itself and forms a loop shape. This can be further divided in to radial loop that points towards the thumb or ulnar loop that points towards the ulna bone. These loop patterns form the majority of the fingerprint (60%).

Whorls: These are circular patterns similar to whirlpools. They can be plain or concentric whorls, a central pocket loop that is a loop with a whorl at one end, a double loop (two loops in a S-shaped pattern), or accidental loop that carries an irregular shape. These patterns constitute about 35% of a person’s fingerprint.

Arches: These are wave-like and consist of plain arches and bent arches that rise to a sharper point compared to plain arches. These patterns form 5% of the fingerprint.

Fingerprint persistent patterns

These patterns remain consistent with age. Studies conducted over decades show that these patterns remain unchanged throughout a person’s life. Even in cases where new skin develops, it forms in the existing ridge and furrow patterns already established in the finger. In cases where the skin is damaged, the new skin also follows previous patterns.

The above-mentioned patterns are used to include or exclude a fingerprint from the analysis. The fingerprint analyst uses specific points on the ridge to identify and compare similar points on an unknown fingerprint. If a significant number of points correlate between the two fingerprints then they are said to be of the same person.

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Fingerprints can be found on practically any solid surface, including the human body. Analysts classify fingerprints into three categories according to the type of surface on which they are found and whether they are visible or not.

The Fingerprint Analysis Process

ingerprint examiners use the ACE-V (analysis, comparison, evaluation and verification) method to reach a determination on each print.

Analysis involves assessing a print to determine if it can be used for a comparison. If the print is not suitable for comparison because of inadequate quality or quantity of features, the examination ends and the print is reported as not suitable. If the print is suitable, the analysis indicates the features to be used in the comparison and their tolerances (the amount of variation that will be accepted). The analysis may also uncover physical features such as recurves, deltas, creases and scars that help indicate where to begin the comparison.

Comparisons are performed by an analyst who views the known and suspect prints side-by-side. The analyst compares minutiae characteristics and locations to determine if they match. Known prints are often collected from persons of interest, victims, others present at the scene or through a search of one or more fingerprint databases such as the FBI’s Integrated Automated Fingerprint Identification System (IAFIS). IAFIS is the largest fingerprint database in the world and, as of June 2012, held more than 72 million print records from criminals, military personnel, government employees and other civilian employees.

Evaluation is where the examiner ultimately decides if the prints are from the same source (identification or individualization), different sources (exclusion) or is inconclusive. Inconclusive results may be due to poor quality samples, lack of comparable areas, or insufficient number of corresponding or dissimilar features to be certain.

Verification is when another examiner independently analyzes, compares and evaluates the prints to either support or refute the conclusions of the original examiner. The examiner may also verify the suitability of determinations made in the analysis phase.