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Strengthening Forensic Science in the United States: A Path Forward
scription of the steps of ACE-V and an analysis of its limitations is provided in a paper by Haber and Haber.22
Although some Automated Fingerprint Identification Systems (AFIS) permit fully automated identification of fingerprint records related to criminal history (e.g., for screening job applicants), the assessment of latent prints from crime scenes is based largely on human interpretation. Note that the ACE-V method does not specify particular measurements or a standard test protocol, and examiners must make subjective assessments throughout. In the United States, the threshold for making a source identification is deliberately kept subjective, so that the examiner can take into account both the quantity and quality of comparable details. As a result, the outcome of a friction ridge analysis is not necessarily repeatable from examiner to examiner. In fact, recent research by Dror23 has shown that experienced examiners do not necessarily agree with even their own past conclusions when the examination is presented in a different context some time later.
This subjectivity is intrinsic to friction ridge analysis, as can be seen when comparing it with DNA analysis. For the latter, 13 specific segments of DNA (generally) are compared for each of two DNA samples. Each of these segments consists of ordered sequences of the base pairs, called A, G, C, and T. Studies have been conducted to determine the range of variation in the sequence of base pairs at each of the 13 loci and also to determine how much variation exists in different populations. From these data, scientists can calculate the probability that two DNA samples from different people will have the same permutations at each of the 13 loci.
By contrast, before examining two fingerprints, one cannot say a priori which features should be compared. Features are selected during the comparison phase of ACE-V, when a fingerprint examiner identifies which features are common to the two impressions and are clear enough to be evaluated. Because a feature that was helpful during a previous comparison might not exist on these prints or might not have been captured in the latent impression, the process does not allow one to stipulate specific measurements in advance, as is done for a DNA analysis. Moreover, a small stretching of distance between two fingerprint features, or a twisting of angles, can result from either a difference between the fingers that left the prints or from distortions from the impression process. For these reasons, population statistics for fingerprints have not been developed, and friction ridge analysis relies on subjective judgments by the examiner. Little research
L. Haber and R.N. Haber. 2008. Scientific validation of fingerprint evidence under Daubert. Law, Probability, and Risk 7(2):87-109.
I.E. Dror and D. Charlton. 2006. Why experts make errors. Journal of Forensic Identification 56(4):600-616.