1. Fingerprints and Identity: Exploring the Validity and Certainty of Identification
Karrie L. Casada
University of California, Irvine
Undergraduate Research Symposium
May 15, 2004
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2. Key Definitions Automated Fingerprint Identification System AFIS
Ten-Print or Rolled Impressions
Latent Prints
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3. Key Definitions (cont.)
Candidate list
Hit
Match
Minutia
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4. Look to the past….
Fingerprint evidence has been used for over 100 years
Accepted without challenge
Not tested
Become part of our belief of reliable forensic evidence
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5. …and the evidence is flawed
How do we know it is reliable?
How many people have been put in jail because of fingerprint evidence?
What if we are wrong?
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6. Past research: Uniqueness
Most research supports uniqueness
Uniqueness if often used to explain accuracy and validity
Since fingerprints are created in the womb, they are permanent and unique (Babler, 1987)
Because they are permanent and unique, the error rate is zero (Wertheim, 2001)
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7. Past research: Uniqueness (cont.)
Uniqueness cannot account for accuracy or validity
The question is not about uniqueness but about human error: how much similarity exists between prints that might hinder distinguishing one print from another?
How can an subjective observation lead to an absolute identification?
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8. Past research: Accuracy & Validity
Since 1892, ten statistical models have been presented in an attempt to provide a probabilistic model for fingerprint individuality (Stoney, 2001)
Each model has flaws that damage the approach irrevocably
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9. Past research: Accuracy & Validity (Cont.)
“From a statistical viewpoint, the scientific foundation for fingerprint individuality is incredibly weak”
“None of the models (have) been subjected to testing, which is of course the basic element of the scientific approach”
(Stoney, 2001)
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10. Past research: Proficiency Testing
The International Association for Identification (IAI) certifies individual fingerprint examiners: pass rate of 50%
The American Society of Crime Laboratory Directors (ASCLD): 20% of the examiners made an erroneous identification
(Haber and Haber, 2003)
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11. Past research: Proficiency Testing (cont.)
Examiners are not required to be certified to be deemed an expert in a courtroom
Test does not mimic real life identifications
Use of clean, clear test prints
Lack of blind testing
Lack of generalalizablity
Lack of AFIS
(Haber and Haber, 2003)
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12. Past research: Proficiency Testing (cont.)
This “matching” game does not produce a zero error rate for examiner accuracy
“If these comparisons had been presented in court as testimony, one in five latent print examiners would have provided damning evidence against the wrong person”
(Haber and Haber, 2003)
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13. Past research: AFIS
Meagher (2002), testifying on behalf of the FBI, estimated that 50% of fingerprint comparisons use AFIS
“There are no published experimental tests on the accuracy with which human examiners compare latent prints to AFIS outputs, nor any on the effect of the number of candidates produced by AFIS on the accuracy of comparison” (Haber and Haber, 2003)
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14. Past research: AFIS (cont.)
FBI 50K study
Copy of database print used as search print
Searching for an exact duplicate
Latent search print was a cropped section of database print
Still searching for an exact duplicate
(Kaye, 2002)
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15. Past research: AFIS (cont.)
“This number, 1097, is extremely large. We have no word for this number in any language, as it is beyond human comprehension. In the entire history of mankind, there have been only about 1011 fingerprints. It is possible that in the entire future of all mankind there will never be 1097 fingerprints” (Wayman, 2000)
Because neither the method nor the calculations were made available, scholars can only guess as to how the final results were reached (Stoney, 2001)
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16. Past research: AFIS (cont.)
Test produced an unusual high Z score for 3 comparisons
3 prints were duplicates
3 prints were discarded
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17. Past research: AFIS (cont.)
The fingerprint community and scholars are aware that no two impressions obtained from rolled or latent prints from the same finger are exactly alike
In real world fingerprint comparisons, a print would never be compared to itself
Flawed statistical methods
Test and its results were never published
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18. Past research: AFIS (cont.)
“…experimental tests are needed to demonstrate the accuracy with which examiners make identifications and elimination using AFIS outputs. Until such data is available, identifications made in court based on AFIS search outputs will continue to pose special concerns about error rates. At present, there are no data” (Haber and Haber, 2003)
“…the real issue is whether fragments of prints, or smeared prints, or layers of prints one upon another, can be accurately linked to one and only one person on earth. It is time to examine the court’s antipodal opinions on this issue” (Kaye, 2003)
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19. Current Study Overview
Collect ten-prints
Collect latent prints
All prints are numerically linked
Create an AFIS database
Run searches
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20. Hypotheses H1: Can a candidate be located for each search print?
H2: Is the first candidate the match?
H3: Can a statistical probability be derived?
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21. Methodology Ten-print cards collected: 166 Latent prints collected:
371
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22. Methodology (cont.)
Ten-prints scanned into AFIS creating a searchable database
Ten-prints prints are “auto extracted”
Latent prints used as search prints
Candidate list analyzed
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23. Results H1: Although each latent print has a
corresponding ten-print card in the system, 31% had “no hit”
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24. Results (cont.) H2: Although each latent print has a
corresponding ten-print card in the system,
60% had the correct candidate “hit” in the #1 position
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25. Results (cont.)
H3: Based on the points used to locate the correct match print, perhaps a statistical probability can be developed
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26. Discussion
Latent prints that mimic real-life crime scene prints are key to any fingerprint research
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27. Discussion (cont.) Error rate is not zero
If examiners rely on the first “match,” they might be excluding the correct candidate
AFIS is a screening tool
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28. Discussion (cont.) Accuracy dependent on quality prints
Certainty is dependent on examiner abilities
Uniqueness theory can hinder proper identifications
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29. Perspective
Small database
Peer review to explore
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30. Future research Amount of detail needed for a match
The role of minutia points
Examiners ability to interpret a candidate list
Examiner bench note availability as courtroom evidence
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31. Acknowledgements Dr. Simon Cole Dr. Valerie Jenness UROP AFIX Tracker
Social Science Lab
Volunteer subjects
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