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Kamis, 31 Juli 2014

The FBI's Worst Hair Days

An article by Spencer Hsu in yesterday's Washington Post suggests that the FBI lost a tug of war within the Justice Department. In 2012, the Bureau commenced a comprehensive review of the testimony of FBI hair analysts about matches to defendants in criminal cases before 2000. In those pre-DNA-evidence days, microscopic hair comparisons were valuable for seeing whether a suspect could be the source of a hair at a crime scene. (They still are, but the FBI now uses mitochondrial DNA testing to demonstrate a positive association and relies on visual comparison to screen out nonmatching hairs.)

Clearly, an inclusion—that is, two hairs with a similar set of features—was never definitive. Even hairs from the same individual vary in certain respects. But hairs from the same individual are more likely to "match" than hairs from different individuals. Thus, a careful hair analyst should have reported a negative finding as an exclusion and a positive finding with words like "not excluded," "could have," "consistent with," or "match, but."

After it became apparent that the FBI’s analysts were not always being this careful, the Department of Justice agreed to “identify[] historical cases for review where a microscopic hair examination conducted by the FBI was among the evidence in a case that resulted in a conviction ... with the goal of reaching final determinations in the coming months.” That was 2012. The Post article reports that in 2013, the FBI stopped the reviews. It started them back up this month, on orders from the Deputy Attorney General.

The FBI attributes the delay, in part, to “a vigorous debate that occurred within the FBI and DOJ about the appropriate scientific standards we should apply when reviewing FBI lab examiner testimony — many years after the fact.” To get a sense of what this debate might have been about, it may be useful to examine the two specific cases mentioned in the Post article on “forensic errors.”

The Exoneration of Santae Tribble

The article includes an imposing photograph of Santae A. Tribble. The caption explains that Tribble, who was convicted in Washington, D.C., at age 17, “spent 28 years in prison based largely on analysis of hairs found at the scene of a taxi driver’s murder in 1978. More advanced DNA testing showed that none of the hairs used as evidence shared Tribble’s genetic profile. A judge has vacated his conviction and dismissed the underlying charges.”

There is no denying that evidence suggesting that an innocent man is guilty is erroneous, but is it a laboratory error? Some people argue that microscopic hair evidence is unvalidated and because it sometimes incriminates innocent people, it should be inadmissible. But if that is correct, why go through the trouble of reviewing all the cases? The FBI could just send out letters in every case saying that the laboratory no longer stands by the unvalidated testimony its examiners gave.

Surely there was (and is) some useful information in microscopic hair comparisons. A 2002 FBI study showed that DNA testing confirmed most visual microscopic associations (almost 90%) on a sample of hairs from casework. For a small minority of hair comparisons—as in Mr. Tribble’s case—microscopy produced false positives.The specificity of the technique—like that of drug tests, tests for strep throat, and so many other things—is not 100%.

Inasmuch as all hair comparisons cannot summarily be dismissed as invalid, what makes the comparison in the Tribble case a departure from the FBI calls “appropriate scientific standards”? An article from the National Association of Criminal Defense Lawyers (NACDL), which is cooperating in the process of reviewing the cases, describes the criteria as follows:
Error Type 1: The examiner stated or implied that the evidentiary hair could be associated with a specific individual to the exclusion of all others.

Error Type 2: The examiner assigned to the positive association a statistical weight or probability or provided a likelihood that the questioned hair originated from a particular source, or an opinion as to the likelihood or rareness of the positive association that could lead the jury to believe that valid statistical weight can be assigned to a microscopic hair association.

Error Type 3: The examiner cites the number of cases or hair analyses worked in the lab and the number of samples from different individuals that could not be distinguished from one another as a predictive value to bolster the conclusion that a hair belongs to a specific individual.
Which of these errors did the FBI laboratory commit in Mr. Tribble’s case? According to an earlier Post article on the case, “A police dog found a stocking on a sidewalk a block away [from the victim’s body]. Months later, the FBI would report that a single hair inside it matched Tribble’s ‘in all microscopic characteristics.’” Ideally, the analyst would have added that hair from other people also could have matched, or, at the least, defense counsel should have elicited this fact on cross-examination.

No such significant qualifications or caveats emerged. Instead, according to the Innocence Project, the FBI analyst "testified that one of the hairs from the stocking mask linked Tribble to the crime." The National Registry of Exonerations reports that he "said ... the hair in the stocking came from Tribble." Such testimony seems to be an "Error Type 1," although it is not clear from these descriptions whether the "link" was explicitly "to the exclusion of all others."

The latter phrase was extremely popular among analysts of impression and patterns (like fingerprints and toolmarks) who believed that their disciple studies characteristics that can exist in their particulars in only one object in the universe. Of course, the words "to the exclusion" are logically redundant. If the analyst believed that "the hair ... came from Tribble," then he must have believed that it did not come from anyone else. But one can believe that a named individual is the source of a trace (because that is the most likely conclusion) without believing it is impossible for anyone else to have been the source (which is, I think, is what "to the exclusion" was supposed to mean).

Thus, there is an ambiguity in the meaning of an "Error Type 1." How explicit must the analyst be in excluding all other individuals as contributors of the hair? The NACLD's description of the criteria indicates that a literal use of the phrase is not critical. The article illustrates the error with the following, hypothetical testimony:
I found brown, Caucasian head hairs on two items of clothing, the sports coat, and a pair of slacks that were reported to me as belonging to (the defendant). Now, these hairs matched in every observable microscopic characteristic to that known hair sample of DEC (the decedent) and consistent with having originated from her. In my opinion, based on my experience in the laboratory and having done 16,000 hair examinations, my opinion is that those hairs came from DEC.
But regardless of whether Tribble's trial testimony included an "Error Type 1" as the FBI has defined the errors, it was excessive. The analyst should have stuck to reporting the results of the comparison and not made a source attribution.

In addition to the analyst's overstated testimony, the prosecutor came vanishingly close to making the “Error Type 2.” He argued in closing that “There is one chance, perhaps for all we know, in 10 million that it could [be] someone else’s hair.”

In the end, however, what exonerated Tribble was not the recognition of the hyperbole of the expert and the prosecutor, but the proof from a DNA test that the hair on the stocking probably worn by the actual murderer was not his.

The Conviction of John Duckett

The second case of "forensic error" discussed in the Post article is the trial of James Duckett, a former police officer in Florida. The Post article cites this case as an example of “the continued inadequacy of officials’ response.”

Duckett was convicted and sentenced to death for sexually assaulting, strangling, and drowning an 11-year-old girl. Unlike Tribble, Duckett has not proved actual innocence. Without such proof, even a letter from the FBI disowning some parts of the testimony in the case may not be a get-out-of-jail card.

The analyst in the case was the now notorious Michael Malone. The Post notes that Malone was "discredited in a 1997 inspector general’s report on misconduct at the FBI lab." This report came about nine years after Duckett's conviction, and Duckett made sure the Florida courts heard about it. At the center of Duckett's latest postconviction motion was a report from an expert who had been hired by the FBI in response to the first OIG report to "review[] many cases—particularly death penalty cases—in which Malone offered expert testimony." This expert was sharply critical of Malone's documentation of his work and the unsupportable "degree of analytical certainty" with which Malone testified about the hairs in Duckett's case.

Would a speedier review on the FBI's part have made a difference? I doubt it and have juxtaposed some of the Post’s description of the case with the court’s to indicate why.


Duckett, then a rookie police officer in Mascotte, Fla., was convicted of raping and strangling Teresa McAbee, 11, and dumping her into a lake in 1987.

... Malone ... testified at trial that there was a “high degree of probability” that the hair came from Duckett.

Such testimony is scientifically invalid, according to the parameters of the current FBI review, because it claims to associate a hair with a single person “to the exclusion of all others.”

The Florida court denied Duckett’s request for a new hearing on Malone’s hair match. The court noted that there was other evidence of Duckett’s guilt and that the FBI had not entirely abandoned visual hair comparison.
Malone also explained that hair analysis is not as precise as fingerprints for identifying someone. Malone expressly stated that he could not say that a particular hair came from a specific person to the exclusion of anyone else.

(1) [T]he victim was last seen in Duckett's patrol car; (2) the tire tracks at the murder scene were consistent with those from Duckett's car; (3) no one saw Duckett, the only policeman on duty in Mascotte, from the time he was last seen with the victim until the time he met the victim's mother at the police station; (4) numerous prints of the victim were found on the hood of Duckett's patrol car, although he denied seeing her on the hood; (5) a pubic hair found in the victim's underpants was consistent with Duckett's pubic hair and inconsistent with the others in contact with the victim that evening; and, (6) during a five-month period, Duckett, contrary to department policy, had picked up three young women in his patrol car while on duty and engaged in sexual activity with one and made sexual advances toward the other two.

Of course, the arguably redeeming parts of Malone's testimony and the state's other evidence of guilt do not condone or excuse any foot dragging by the FBI, but they do indicate the complexities that can arise in untangling the consequences of analysts' overstated testimony.

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