Comedic License

The other day, I mentioned a satire by the comedian John Oliver on developments in forensic science. A few minutes of the video was played for an international audience at Harvard Law School on October 27 in the introduction to a panel discussion entitled "Evidence, Science, and Reason in an Era of 'Post-truth' Politics." The clip included remarks from Santae Tribble and his lawyer about hair evidence in the highly (and deservedly) publicized exoneration of Mr. Tribble. 1/ I got the impression from the Oliver video that an FBI criminalist claimed that there was but a 1 in 10 million chance that the hair could have come from anyone else. In Oliver's recounting of the case,

Take Santae Tribble, who was convicted of murder, and served 26 years in large part thanks to an FBI analyst who testified that his hair matched hair left at the scene, and he will tell you the evidence was presented as being rock solid. "They said they matched my hair in all microscopical characteristics. And that's the way they presented it to the jury, and the jury took it for granted that that was my hair."

You know, I can see why they did. Who other than an FBI expert would possibly know that much about hair? ... Jurors in Tribble's case were actually told that there was one chance in ten million that it could be someone else's hair.

I have not seen the trial transcript, but a Washington Post reporter, who presumably has, provided this account:

In Tribble’s case, the FBI agent testified at trial that the hair from the stocking matched Tribble’s “in all microscopic characteristics.” In closing arguments, federal prosecutor David Stanley went further: “There is one chance, perhaps for all we know, in 10 million that it could [be] someone else’s hair.” 2/

If the Post is correct, it was not "an FBI expert" who "actually told" jurors that the probability the hair was not Tribble's was 1/10,000,000. It was an aggressive prosecutor who made up a number that he imagined "perhaps ... could" be true. Like the similar figure of 1/12,000,000 in the notorious case of People v. Collins, 438 P.2d 33 (Cal. 1968), this number plainly was objectionable.

In distinguishing between the criminalist's testimony and the lawyer's argument, I do not mean to be too critical of Oliver's condensed version and passive voice. Sometimes a little oversimplification saves a lot of pedantic explanation. The sad fact is that, whichever participants in  the trial were responsible for the 1/10,000,000 figure, Tribble's case exemplifies Oliver's earlier observation that "[t]he problem is, not all forensic science is as reliable as we have become accustomed to believing. ,,, It's not that all forensic science is bad, because it's not. But too often, its reliability is dangerously overstated ... ." 3/

NOTES

1. See The FBI's Worst Hair Days, July 31, 2014, Forensic Sci., Stat. & L., http://for-sci-law.blogspot.com/2014/07/the-fbis-worst-hair-days.html
2. Spencer S. Hsu, Santae Tribble Cleared in 1978 Murder Based on DNA Hair Test, Wash. Post, Dec. 14, 2012, https://www.washingtonpost.com/local/crime/dc-judge-exonerates-santae-tribble-of-1978-murder-based-on-dna-hair-test/2012/12/14/da71ce00-d02c-11e1-b630-190a983a2e0d_story.html?utm_term=.9dc9725b8b98 (emphasis added).
3. Cf. David H. Kaye, Ultracrepidarianism in Forensic Science: The Hair Evidence Debacle, 72 Wash. & Lee L. Rev. Online 227 (2015), ssrn.com/abstract=2647430

POSTSCRIPT

After composing these remarks, I located the 2012 motion to vacate Tribble's conviction. (Motion to Vacate Conviction and Dismiss Indictment With Prejudice on the Grounds of Actual Innocence Under the Innocence Protection Act, United States v. Tribble, Crim. No. F-4160-78 (D.C. Super. Ct. Jan. 18, 2012), available at http://www.pdsdc.org/docs/default-source/default-document-library/motion-to-vacate-conviction-on-the-grounds-of-actual-innocence-january-18-2012.pdf?sfvrsn=814394d0_0.) This document contains more extended excerpts from the trial transcript, These indicate that although the FBI agent, James Hilverda, did not generate a nonsource probability of 1/10,000,000, he did insist that it was at least "likely" that Tribble was the source, and he indicated that the probability of a coincidental match could be on the order of one in a thousand.

TESTIMONY OF JAMES HILVERDA
Q. Is it possible that two individuals could have hairs with the same characteristics?
A. It is possible, but my personal experience, I rarely have seen it. Only on very rare occasions have I seen hairs of two individuals that show the same characteristics. Usually when we find hairs that we cannot distinguish from two individuals, it is due to the fact that the hairs are either so dark that you cannot see sufficient characteristics, or they are too light that they do not have very many characteristic[ s] to examine. So you cannot make a real good analysis in that manner. But there is a potential even with sufficient characteristics to once in a while to see hairs that you cannot distinguish.
Q. And is it because of that small possibility that two hairs can be from different people that you never give absolutely positive opinion that two hairs, in fact, did come from the same person.
A. That is correct.
...
Q. If you compare them and they microscopically match in all characteristics, could you say they could have come from the same person?
A. That's correct.
Q. Have you ever seen two hairs from two. different people that microscopically match?
A. Well, it is possible in the thousands of hair examples I have done, it is very, very rare to find hairs from two different people that exhibit the same microscopic characteristics. It is possible, but as I said, very rare.
...
A. ... I found that these hairs — the hairs that I removed from the stocking matched in all microscopic characteristics with the head hair samples submitted to me from Santae Tribble. Therefore, I would say that this hair could have originated from Santae Tribble.
Q. Is there any microscopic characteristics [sic] of the known hair that did not match?
A. No. The hair that I aligned with Santae Tribble matched in all microscopic characteristics, all characteristics were the same.
Q. And were there a large number of characteristics which were the same or—
A. All the characteristics were the same and there was a sufficient number of characteristics to allow me to do my examinations.
...
A. ... I think you can identify individuals, say, as to race, you can an [sic] indication that it came from an individual because it matches in all characteristics and I would say that when I have-in my experience that I feel when I have made this type of examination, it is likely that it came from the individual which I depicted it as coming from.
...
ASSISTANT UNITED STATES ATTORNEY DAVID STANLEY ARGUED:
Mrs. McCormick said at least one of the robbers, the only one that she saw, was wearing a stocking mask. A block from where that homicide occurred, more or less, through the alley and around the corner on a fresh trail found by a trained canine dog, was found what, a stocking mask. In that stocking mask was found what, a hair.
Now whose hair was that? Well it was compared by the FBI laboratory and they can say for one thing, it wasn't Cleveland Wright's hair. They can say that that hair matched in every microscopic characteristic, the hair of Santae Tribble. Now for scientific reasons, which were explained, they cannot say positively that that is Santae Tribble's hair because on rare occasions they have seen hairs from two different people that matched. But usually that is the case where there have been few characteristics present. Now Agent Hilverda told you that on these hairs, the known hairs of Santae Tribble and the hair found in the stocking, there were plenty of characteristics present, not that situation at all. But because the FBI is cautious, he cannot positively say that that is Santae Tribble's hair.
DEFENSE COUNSEL ARGUED:
Well what did Special Agent Hilverda say, microscopic analysis. Throwing the large terms away, what did he say? "Could be." He looked at one hair, he looked at Santae Tribble's hair and said, could be.
AUSA STANLEY ARGUED:
[T]he dog found a stocking with a hair which not only could be Santae Tribble's, it exactly matches Santae Tribble's in every microscopic characteristic. And Mr. Potenza says throw away all the scientific terms and reduce it to "could be." Scientific terms are important He told you how he compares hairs with powerful microscopes. It is not just the color or wave. He could reject Cleveland Wright's hair immediately; it wasn't Cleveland Wright's hair in that stocking. But he couldn't reject Santae Tribble's because it was exactly the same. And the only reason he said could be is because there is one chance, perhaps for all we know, in ten million that it could [be] someone else's hair. But what kind of coincidence is that?
... The hair is a great deal more than "could be." And if you listened to Agent Hilverda and what he really said, the hair exactly matched Santae Tribble's hair, found in the stocking.