CSI failure: Hair sample evidence

Hair sample testing

You’ve seen it on TV. The CSI’s arrive at a crime scene and collect a little tiny piece of trace evidence in a small glass jar. When they get back to the lab they put the little piece of hair into the hairalizer lab machine and press a button. Then they stand around having a funny conversation while they wait for the report to print out next to them. When it does, the hair sample always turns out to be a perfect match to the perpetrator they never suspected. They got him! Except that, and I don’t mean to ruin those shows for you, that’s not the way it works in real life. There is no ‘hairalizer’ machine and it turns out there really isn’t any significant science behind hair analysis at all.

In fact, the FBI recently announced that it will start an extensive review of hair sample evidence from more than 2,000 cases going back as far as 1985. The review is restricted to cases in which the hair sample evidence was introduced as evidence and central to the conviction of the defendant, including in death penalty cases. In two unusual moves, the U.S. Department of Justice is waiving the normal deadlines for appeals in order to, in their own words, give “wrongly convicted people a fair chance of review” and will examine old death penalty cases in which the person was executed in part because of hair analysis testimony.

So what is the big deal, you ask? At its simplest level hair sample analysis is the testing of hair found at the scene of a crime for the presence of chemicals such as illegal drugs or specific minerals etc. and attempting to match the sample to a defendant. Sometimes the analysis also refers to microscopic analysis or comparison of two hair samples to try to place the defendant somewhere or to prove identity. Of course hair itself does not contain DNA. It’s made of a fibrous protein called keratin. You can’t genetically match a person using keratin samples unless you get enough of the hair follicle attached to the hair with cells that contain DNA. Sometimes the FBI puts all kinds of effort and money into trying to find that little tiny needle of DNA in the huge haystack of the hair shaft, but it’s not at all common to find anything.

Hair graphicWhile there may be something to the scientific idea of testing hair material for the presence of things like illegal drugs in our bloodstream that get absorbed by the hair as it grows out of our bodies, there are all kinds of problems:

  • Most commercial hair analysis laboratories have not validated their analytical techniques by checking them against standard reference materials. The techniques typically used to prepare samples for analysis can introduce errors for many of the elements being determined.
  • Hair is thin and affected by exposure to various substances such as shampoos, bleaches, work environments, substances in hats, and hair dyes. No analytic technique enables reliable determination of the source of specific levels of elements in hair as either bodily or environmental in origin.
  • The level of certain minerals can be affected by the color, diameter and rate of growth of an individual’s hair, the season of the year, the geographic location, and the age and gender of the individual.
  • Normal ranges of keratin chemical composition has not been defined.
  • For most elements, no correlation has been established between hair level and other known indicators of nutrition status. It is possible for hair concentration of an element (zinc, for example) to be high even though deficiency exists in the body.
  • Hair grows slowly (about one centimeter per month), so even hair closest to the scalp is several weeks old and thus may not reflect current body conditions for purposes of health diagnosis or matching of samples.
  • Hair could get mixed by normal environmental conditions and the results could be a blend of several individuals without reliable ways of separating similar samples.

This is not an exclusive list, just representative of the kinds of problems “hair testing experts” face when doing their thing. In fact, the American Medical Association says that hair analysis for medical therapy is an “unproven practice with potential for healthcare fraud.” Most insurance companies do not pay for hair analysis except for arsenic tests which speaks volumes. The issue the FBI may have is that their lab techs might have represented the testing techniques as conclusive or more reliable than what it actually is.

Hair sample testSo, the FBI decided to study “whether analysts exaggerated the significance” of the samples, or in some cases reported the results inaccurately. The FBI says “there is no reason to believe the FBI Laboratory employed ‘flawed’ forensic techniques,” and that microscopic hair analysis is “a valid forensic technique and one that is still conducted at the lab” alongside DNA testing.

Apparently “the purpose of the review is to determine if FBI Laboratory examiner testimony and reports properly reflect the bounds of the underlying science.” That’s just about as telling as saying ‘our people may have screwed up and this stuff doesn’t really work.’ And it’s significant because according to the Innocence Project – famous for pushing for the release of prisoners exonerated by DNA testing – almost a quarter of individuals exonerated by DNA evidence were originally convicted in part thanks to microscopic hair analysis. Some had died in custody. It’s about time the FBI did a bit of a review of this CSI technique.

-Samuel Owen

© Samuel Owen 2013. All rights reserved. Please read important notices and disclaimers by clicking here.

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