Validity, Overclaiming, and Error: More on Willie Manning's Exoneration

Yesterday I questioned reliance on the exoneration of Willie Manning as a case in which hair evidence was severely undermined, prompting his exoneration. The problem with this understanding of the Manning exoneration is that the crimes for which his conviction was overturned did not involve any hair evidence. In addition, I tried to probe what Department of Justice reported was erroneous or invalid about the hair evidence against him in a separate case. I concluded with the observation that

It is entirely possible that DNA testing will soon exonerate Manning in the Miller-Steckler murder case (to the extent of showing that the hair in the car was not his). As of May, 2015, this had not happened. If it does, it would mean that either the original determination of the racial characteristics of the hair was wrong -- something that the FBI has not conceded -- or that the determination was correct but that Manning was not the person whose hairs were in the car -- something that the criminalist never purported to resolve.

Scott Henson, "a former journalist turned opposition researcher/political consultant, public policy researcher and blogger who is presently Executive Director of the Innocence Project of Texas" 1/ and whose Grits for Breakfast blog is a great source of information with a Texas flavor, made an important comment:

Perhaps that's "something that the criminalist never purported to resolve," but posing that implication is of course the reason the prosecutor presented his or her testimony. When they're reviewing these cases, the issue isn't just whether the forensic examiner erred but also if prosecutors overstated or misused the evidence to ask the jury to draw invalid conclusions. (In Texas' review of state-level examiners, with which I'm more familiar, they examine both the forensic testimony AND the prosecutor's closing arguments.)

If the DNA testing comes back excluding Manning, IMO it'd be fair to say that the use of hair testimony in his case has been "severely undermined," since it would have treated exculpatory evidence as inculpatory.

Overstating the scientific findings by experts or parties is a major problem. The Santae Tribble case is a glaring example of prosecutorial overclaiming. The Assistant US Attorney told the jury that "[t]here is one chance, perhaps for all we know, in 10 million that it could [be] someone else’s hair." But published estimates of the probability that hairs from different individuals will be classified as microscopically similar range from 1/4500 to 1/10 (with the latter being much more plausible). Closing arguments like this are therefore unacceptable. If courts permit hair evidence to be used, then a prosecutor who does so has a duty to use it only for what what it is worth. In Tribble, the prosecutor claimed that the hairs had matching features and then overclaimed that the probability of this match was negligible if it was someone else's hair.

The odd thing about the Manning case in which hair evidence played a role, however, is that the overclaiming did not relate to the claim. The overclaiming that the FBI spotted in its hair evidence review project pertained to the ability to identify individuals by a combination of many physical characteristics of hair. But the expert expressly stated that that could not be done in this case and only made a claim about race.

Could the prosecutor have gone beyond the expert's testimony about race and "overstated or misused the evidence to ask the jury to draw invalid conclusions"? Yes, that could be. The FBI's hair review project is limited to the reports and testimony of FBI hair examiners. It will be interesting to see whether states implement hair evidence review projects and what their scope will be.

Whether or not there was any relevant overclaiming in Manning, it is true that a DNA test showing that the hair is not Manning's would severely undermine the state's case. But it would not necessarily undermine the validity of the examiner's testimony that the hair had certain "racial characteristics." (Whether, as the DOJ letter indicated, racial classifications are valid to begin with is, of course, a different question.) 2/

To see that disproof of an inference from scientific evidence that arises from better scientific evidence does not make the original evidence invalid, let's switch from hair to serology for a moment. Sometimes hair can be analyzed for ABO blood groups. As a thought experiment, suppose that the testimony had not been about race but was only that both Willie Manning and the hair in the car were blood group B, and that Manning was among the 10% or so of the U.S. population whose ABO type is consistent with this finding. Would a later mitochondrial DNA test that excluded Manning severely undermine this ABO testimony? It certainly would contradict the conclusion that Manning left hairs in the car. It would change the hair evidence from inculpatory to exculpatory.

But it would not show that ABO testing is invalid in general or that the value of the test was overstated in this case. It would be a reason to exonerate Manning but not a reason to denominate the original evidence as scientifically invalid or as having exceeded the limits of science. In this respect, it would be no different than incontrovertible evidence that Manning was incarcerated when the murders were committed -- powerful evidence of innocence but no evidence of invalidity or overclaiming.

NOTES

1. Scott Henson, Who Is This Guy?, Grits for Breakfast, Jan. 6, 2004, http://gritsforbreakfast.blogspot.com/2005/01/about-me.html
2. For a short, sympathetic review of the theory of racial classification of hairs, see Edward J. Imwinkelried, Forensic Hair Analysis: The Case Against the Underemployment of Scientific Evidence, 39 Wash. & Lee L. Rev. 41, 49-50 (1982).

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