Fingerprints should not imply uniqueness

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For over 100 years, fingerprint evidence has been used as a valuable tool for the criminal justice system. Relying on the generalized premise of “uniqueness”, the forensic community has regarded fingerprint evidence as nearly infallible having the capacity to “individualize” the source of a fingerprint impression to a single individual. While the uniqueness of a complete record of friction ridge skin detail is generally undisputed, the extension of that premise to partial and degraded impressions has become a central issue of debate. Nevertheless, forensic science laboratories routinely use the terms “individualization” and “identification” in technical reports and expert witness testimony to express an association of a partial impression to a specific known source. Over the last several years, there has been growing criticism among the scientific and legal communities regarding the use of such terms to express source associations which rely on expert interpretation. The crux of the criticism is that these terms imply absolute certainty and infallibility to the fact-finder which has not been demonstrated by available scientific data. As a result, several authoritative scientific organizations have recommended forensic science laboratories not to report or testify, directly or by implication, to a source attribution to the exclusion of all others in the world or to assert 100% infallibility and state conclusions in absolute terms when dealing with population issues. Consequently, the traditional paradigm of reporting latent fingerprint conclusions with an implication of absolute certainty to a single source has been challenged. The underlying basis for the challenge pertains to the logic applied during the interpretation of the evidence and the framework by which that evidence is articulated. By recognizing the subtle, yet non-trivial differences in the logic, the fingerprint community may consider an alternative framework to report fingerprint evidence to ensure the certainties are not over or understated.


13 thoughts on “Fingerprints should not imply uniqueness

  1. I often see people get confused on this issue. No one disputes that an individual’s fingerprints are unique.

    But criminal forensics are not about that question. Criminal forensics are about an examiner looking at a copy of an impression at a scene and comparing it to an impression of an individual’s fingerprints. That examiner then has to interpret those two impressions and decide if they match. It is that interpretation that has no rigorous science behind it. There are no quality peer reviewed studies about the accuracy of fingerprint interpretation.

    • Fingerprints are different from friction ridges on fingers which create the fingerprints. The friction ridges, if present (some people don’t have them because of injury or disease), are for all practical purposes unique (identical twins frequently have ridges which are very close but still distinct, the last time I heard, in all the cases examined).

      The last time I had formal involvement in the science (and art) was in 2003 so my information may be a obsolete but at that time the FBI used a looser standard for “positive identification” via fingerprints than organizations in western Europe. This always bothered me because of the increased risk of convicting an innocent person.

    • It’s that, and the portrayal of “partial” and “incomplete” fingerprints pulled from evidence (which may have been exposed to degrading elements) as being as infallible and absolutely unique as a full print acquired in a laboratory under ideal conditions.

      The level of certainty on partial prints may meet or exceed the “beyond a reasonable doubt” standard (oft assumed to be 95-99%), but will often fall far short of that, and will certainly NEVER be 100%. The article is calling out forensic analysts who process cases and testify in court as if the partial or latent prints are always 100% unique and certain.

  2. You mean that when we have a hot day in Moscow, Idaho it’s not absolute, conclusive proof of Anthropogenic Global Warming?

    Blasphemer! Science hater!

    • Oh, no, that’s a totally different issue. Of Course a hot day and high-temperature records for that day and site are evidence of global warming and anthropogenic climate change, silly. It’s only the cold-weather records that are just random variations in weather.


        Some 20 years ago I recall weather reports which would give the record high and record low for the day, and the date of that record. This was apparently in the time when the Hockey Stick blade was doing its magic rising inexorably from the handle. I noticed, however, that the record highs for any summer day in Southern California could break any record from 1890, 0920, 1933, 1945 or 1950. Significantly, that day’s hottest did not seem to break any records from the 80’s or the 90’s, which it would if the data were showing a breakout into new territory (i think I learned something from my statistics and investments classes).
        I don’t think the TV weather frogs do that anymore for fear someone else will figure that out.

        • It’s not a total hijack since the subject is the art of science and the science of art, or picking “facts” to reinforce a pre-determined position.

          The actual scientist always asks himself, “Now, how might my assumptions, observations, interpretations of observations or conclusions be wrong?” He will always be able to point to something, that is, unless he’s being paid by interested parties and is too much of a fucking coward to disappoint his benefactors (or financial overlords). The actual scientist will have already made the cases that his harsh critics will have made, prior to presenting his findings to them, because his interest is in discovery and the sharing of discovery rather than status, approval, finding, or some other outcome.

          Actually, Jesus spoke of this directly, but in this enlightened age of peer pressure, pride, fear, doubt, greed and intimidation no one remembers any of it.

  3. dear friends:

    25 years in criminal law, defending and prosecuting for a goodly part of that.–

    fingerprint analysis, and the opinions about identity drawn from it, is not as “subjective” as the discussion in these comments would suggest. it is not done just on the analyst’s bald opinion. or, gut feeling.

    there are a certain number of points of analysis upon which prints are to be examined, and there has to be a positive correlation on a minimum number of such points before a print (and analysis thereof) are admissible in a court proceeding. a “partial,” for instance, which does not meet these minimum points is interesting, and may influence the direction of an investigation, but in and of itself does little to establish guilt or indeed indicate “probable cause” in most instances.

    in short, there is far more discipline in these matters than you credit, and it is not done on one person’s opinion, without review or ability to question.

    john jay

    p.s. i also did quite a lot of work in paternity determination, where dna analysis and dna reports are very important. there is a very famous case out of the tri-cities, in which two males, cousins, both had sexual intercourse with the mother of a child. (i believe the state of washington was looking for contributions to defray “support” payments, that one of the various welfare agencies was paying the mother.) both submitted dna reports. the dna lab returned separate reports, in which the lab stated that it was 99.95% probable that each of them was the father of the child. go figure. in short, nothing is sure in this world, save death and taxes.

    the point is this. the law, nor its practitioners, have never promised absolute certainty in legal disputes, civil or criminal. the law promises only, after consideration of an issue subject to reasonable care in determination of contested facts, a resolution of dispute over those facts. put simply, when you bring a live dispute before a court, the only thing promised is a decision settling the dispute.

    truth is a philosophical and theological question. it has nothing to do w/ the law. the law simply puts an end, or tries to put an end, to argument.

    • The “points of analysis” were just a framework upon which to hang the examiner’s subjective interpretation. Barely a step up from a magician’s patter of “hocus pocus”. An interpretation that still lacked a rigorous scientific foundation upon which to express reliability.

      The probability was being expressed against a random match in the general population. But since the pool of possible fathers was that of two cousins, who likely already shared some DNA, the pool wasn’t randomly selected from the general population and the probability number was meaningless to start with.

    • So, are you saying that once the state proved to 99.95% that it was one cousin or the other it was up to the two men to prove which one was the father? So the state saved the expensive tests for the defendants to pay for.
      And wasn’t that Sommers v Tice all over again (and both about shooting, too!).

    • “the law simply puts an end, or tries to put an end, to argument.”

      That argument sounds all very noble, until you’re the one falsely accused and convicted, which is why have the standards of “innocent until proven guilty” and “proof beyond reasonable doubt”.

      In the case of the cousins, it would have required informing the two labs that cousins were being tested, and giving both labs samples from both fuckers. Just speaking personally, I’d have said they both should support the mother and child, since they both deemed it worth getting their jollies with her, that is, if we’re going to make the issue of who’s penis entered who’s vagina a matter of the state. There’s always the fall back of relying upon the woman’s father, his wisdom, his love for his daughter, and his shotgun to decide the matter, for example.

  4. Did everybody miss it or is it just me. The problem is not in the use of finger printing or the methods or the science. The problem is with the terms “individualization” and “identification” right?

    One of my favorite questions is; “who stands to benefit?”

    Well, if finger prints are “not 100 percent reliable” then the DNA industry and team tyranny that wants a DNA database on every man, woman, and child. That’s who benefits.

  5. A lot of forensic “science” is less than 100% accurate….and some fields
    like ‘forensic odontology’ are essentially useless. Virtually ALL court
    testimony from an ‘expert’ is a matter of opinion and the quality of the testimony
    is colored by the training, experience and bias of the alleged expert.

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