Fingerprint Comparison and Identification
Comparison: The observation that two impressions have ridge characteristics of similar shapes that occupy the same relative positions in both patterns (Figure 5.16).
Identification: The process of determining that the same finger made two or more fingerprint impressions based on the friction ridge details of both impressions (Figure 5.17).
When a fingerprint lift is made, the latent print examiner must conduct a comparison, where appropriate, in hopes of effecting an identification. When latent fingerprints are developed, the best choice for comparison will be determined by the latent print examiner. For example, where groups of three fingers are developed and submitted, the likely choice for comparison
Figure 5.59 Spray Small Particle Reagent on wet object.
is the index, middle, and ring fingers. Where loop patterns are submitted, loops opening to the right are probably from the right hand, and loops opening to the left are probably from the left hand. Double loop whorl patterns are most common to the thumbs. Central pocket loop whorls are most common to the ring finger. The index fingers show the widest variation in patterns of all the fingers. There are also characteristics that may indicate to the latent print examiner that in fact the print submitted may not be of a finger but rather from a palm or even a toe or foot. Various characteristics that present themselves on a latent print, to the trained eye, will be indicative of a certain part of the anatomy. This advanced training is crucial to the latent print examiner.
However, if the latent print examiner does not have a known exemplar to compare with, entering the latent fingerprint into the database or AFIS (Automated Fingerprint Identification System) will be the alternative. A short discussion about AFIS is in order at this time. The term AFIS is a misnomer, unfortunately. An AFIS is nothing more than an elaborate filing and searching system. An AFIS does not make identifications. The identification is the purview of the latent print examiner. The latent print examiner enters the appropriate information into AFIS then allows the system to search the database. When the search is complete, AFIS will give a list of potential candidates to search against. That list can be any number designated by the operator of the AFIS. It is then the job of the latent print
Figure 5.60 Rinse Small Particle Reagent on wet object with distilled water.
examiner to begin with the first candidate on the list and use the comparison process until and if identification is rendered. In some instances, identification will not be made. Like anything else, sometimes the appropriate information has not yet been entered into AFIS. Specifically, if a person has not been booked and their fingerprints taken, those prints will not be in the AFIS (Figure 5.15).
Since the advent of AFIS, countless hours of searching have been eliminated. AFIS can now do in seconds what used to take literally months under the manual system of filing and searching. Additionally, partial latent fingerprints can now be searched as a matter of routine. Today, AFIS has become a standard piece of forensic fingerprint identification equipment.
The comparison process that has been established requires diligence and an eye for detail. Trained examiners know the awesome responsibility that
Figure 5.61 Rinse Small Particle Reagent on wet object with distilled water.
Figure 5.62 Results of Small Particle Reagent; photograph lifts and then lift with latent tape or gel lifter or send the object with results to the lab if possible.
Figure 5.63 Process—step one (after photographs) spray enhancement chemical (Amido Black).
has been bestowed on their ability. There are three possible conclusions an examiner may reach: an identification, a nonidentification, or an inconclusive.
Let us first examine the identification or nonidentification and how those conclusions are arrived at. Through a process coined ACE-V, the fingerprint examiner conducts a comparison. The process allows the examiner the ability to conduct a process whereby all of the information presented to the examiner is ingested and evaluated; then a conclusion is
Figure 5.64 Spraying chemical.
arrived at m a hypothesis, if you will. Various levels of information are also incorporated into the comparison process.
A—Analysis: Analysis is based on the initial information presented to the examiner. In the analysis, the examiner makes a determination of the quality of the print based on a myriad of factors such as substrate, matrix, development medium, deposition pressure, pressure distortion, and anatomical aspects. Is the print of sufficient quality and clarity for a comparison and identification (individualization) or elimination?
Figure 5.65 Results from enhancement chemical.
C—Comparison: What information is contained within the print? Information such as pattern type, friction ridges, flexion creases, major ridge deviations, sequence, and how the two compare to the exemplar print are considered.
E—Evaluation: Evaluating all of the information contained in the latent print, specifically the uniqueness and individuality of the print, the clarity, and the quality. Two questions are asked at this juncture:
Note: If the answer is yes to both questions, an opinion of individualization and identification has been formed (a positive identification and individualization). If the answer is no to one or both questions, an opinion of individualization and identification has not been formed (a negative or no identification).
V—Verification: All work, as in any science, must be subject to review. This portion of the process employs such peer review. Consultation with another expert to verify the opinion of the original examiner is undertaken at this point. Should there be disagreement regarding the identification, a third person may be used for verification purposes. Just as in any other science, there may be disagreements. Those disagreements must be resolved before an identification can go forward.
Figure 5.66 Fabric without chemicals.
The examination process is undertaken by various means, including the use of magnifying glasses, comparators, or other means of magnification. The original documents of both the known exemplar and latent are used for purposes of comparison. Copies should not be used to render an identification unless it can be determined that the same high-quality resolution exists between the original and the copy.
As has been alleged in the past, there is a certain numerical requirement needed to affect an identification or individualization. There is no justifiable reason or statistical evidence for a specific numerical requirement to affect identification. Based on the skill and expertise of the examiner, a conclusion will be rendered based on the totality of information presented to the examiner during the comparison process, and not simply a numeric designation. This brings about the question: What if there are differences between the known exemplar and the latent print. Where an unexplained discrepancy exists, the conclusion should be one of nonidentification.
There are many reasons a latent and known print may deviate slightly. However, that deviation does not automatically render the print a
Figure 5.67 Results from enhancement chemical.
Figure 5.68 Area prior to processing with detection chemical.
Figure 5.69 Area when processed with Bluestar, detection chemical.
Figure 5.70 Evaluation of fingerprints.
nonidentification. Earlier in this chapter, there were many factors listed that affect the presence of a latent print. Those same factors may become part of the deviation explanation. That a latent print is not good enough to be used for identification purposes does not mean the print may not be used for elimination purposes. For example, a latent print may not possess sufficient ridge characteristic information to conclude an identification/
Figure 5.71 The identification process. Example of a fingerprint identification exhibit. The typical exhibit should be clear, concise, and uniform. Although there is no specific number of "points" or ridge characteristics, presenting a uniform exhibit makes the information understandable. After all, it is the trier of fact (judge/jury) who will be analyzing the information during the deliberation.
Figure 5.72 Fingerprint identification chart.
individualization, but there may be sufficient information such as pattern type to eliminate a possible subject.
The third type of conclusion that may be reached by the latent print examiner, inconclusive, means that the latent print and/or the known print
Figure 5.73 Fingerprint evaluation process.
possesses insufficient information for a comparison and/or conclusion. Insufficient information may be due to a variety of factors, as stated earlier in the book.
Additionally, in conjunction with ACE-V for the comparison process, the examiner also takes into account three levels of comparison. The three levels are not used as a replacement for ACE-V but rather as a complement. The levels have simply been termed level 1, level 2, and level 3. What does each level represent?
Level 1: Sufficiency and clarity of information confronting the examiner. Is there enough information, pattern type, flow, and ridge characteristics (Galton details) to ensure the quality of the print is a usable print? If the answer to the question is yes, then one can proceed to level 2.
Level 2: Spatial relationship and type of characteristics within the pattern are used to determine that the known and the unknown were made by the same individual.
Level 3: Ridgeology and poroscopy. At this level, the study of the structure of the ridges and the pores within the ridges is undertaken. Level 3 information in the latent print is often absent due to the quality of the print. The lack of level 3 information does not mean an individualization cannot be made. In fact, identification/individualizations are made even in the absence of level 3 information. More often than not, levels 1 and 2 information is the only information that is present for identification/in- dividualization purposes. Where level 3 information presents itself, the information greatly enhances the individualization perspective. When all of the levels of information have been assessed and the ACE-V process has been undertaken, an appropriate conclusion can be arrived at by the latent print examiner.