Fake Cop “Experts”: Yes, Daubert Applies to Them Too – Sort of.

May 4, 2017
By Hanging Out with Carl Gunn


  • District courts are required to play the same screening, “gatekeeping” role for non-scientific experts like law enforcement “experts” that courts are required to play for scientific experts.
  • The court isn’t necessarily required to apply the specific factors listed in Daubert for scientific experts, but it can use those factors if it thinks them appropriate and helpful.
  • There are some Ninth Circuit cases that have reversed based on the erroneous admission of law enforcement “expert” testimony, and remember that the cases that affirm hold only that it was not an abuse of discretion to admit the testimony, so that doesn’t mean the district court was required to rule that way.



In last week’s post, I talked about studies out there raising doubt about some of the traditional subjects of expert testimony that at least purport to be “science,” or at least “forensic science.”  As discussed in that post, even that “scientific” expert testimony is more open to question than courts – and, I’m afraid, some of us lawyers – have assumed.

In this post – and maybe the next couple of posts – I thought I’d talk about an area of “expert” testimony that annoys – and even sometimes outrages – us defense attorneys.  That’s those “law enforcement experts,” with specialized “training” and “expertise” in the practices of various types of criminals – most often drug traffickers and their organizations.  Despite the fact that these “experts” don’t even approach being scientists, they can give “expert” opinion testimony under Rule 702 of the Federal Rules of Evidence, because Rule 702 allows expert testimony based on “scientific, technical, or other specialized knowledge.”  (Emphasis added.)  And cops purport to have “specialized” knowledge that makes them experts even if their knowledge doesn’t have any scientific basis.

Still, the mere fact that courts can let such cop experts testify as experts doesn’t mean courts are required to let them.  The Supreme Court held in Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137 (1999), that the requirements of Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), apply not just to scientific experts who testify based on scientific knowledge, but also to non-scientific experts who testify based on technical or specialized knowledge.  In particular, district courts have to play the same “gatekeeping” role by making a threshold determination that the expert’s opinion “ha[s] a reliable basis in the knowledge and experience of his discipline.”  Kumho Tire, 526 U.S. at 148, 149 (quoting Daubert, 509 U.S. at 592).

There are some caveats established by Kumho Tire and the later Ninth Circuit cases applying it.  When Daubert first came out and we didn’t have Kumho Tire, I remember having great fun trying to cross examine cops and argue to courts about how the cops’ “expert” testimony didn’t even approach satisfying the “Daubert factors” of testing, peer review, knowledge about the rate of error and “standards controlling the technique’s operation,” and whether the “theory or technique” has “general acceptance” within a “relevant scientific community,” Daubert, 509 U.S. at 592-94.  I knew in my heart it didn’t always make sense to apply all of these factors to non-scientific expert testimony, but I also knew – or at least felt – in my heart that – perhaps because these factors didn’t apply – this cop testimony shouldn’t be allowed as “expert” testimony in the first place.

In any event, Kumho Tire followed the first thing I knew in my heart, but not the second thing – holding that the “Daubert factors” don’t apply to all types of expert testimony, but that doesn’t require excluding it.  The Court explained:

Daubert makes clear that the factors it mentions do not constitute a “definitive checklist.”  Id. at 593, 113 S. Ct. 2786.  And Daubert adds that the gatekeeping inquiry must be “‘tied to the facts’” of a particular “case.”  Id. at 591, 113 S. Ct. 2786 (quoting United States v. Downing, 753 F.2d 1224, 1242 (C.A. 3 1985)).  We agree with the Solicitor General [who was maybe looking down the road to protecting the government’s cop “experts”?] that “[t]he factors identified in Daubert may or may not be pertinent in assessing reliability, depending on the nature of the issue, the expert’s particular expertise, and the subject of his testimony.”  Brief for United States as Amicus Curiae.  The conclusion, in our view, is that we can neither rule out, nor rule in, for all cases and for all time the applicability of the factors mentioned in Daubert, nor can we do so now for subsets of cases categorized by category of expert or by kind of evidence.  Too much depends upon the circumstances of the particular case at issue.

Kumho Tire, 526 U.S. at 150 (emphasis in original).

The foregoing comments also suggest district judges – and you in your arguments to them – can consider other factors in addition to or instead of the Daubert factors to the extent they seem appropriate.  And on the other side of the coin, the comments in Kumho Tire don’t mean none of the Daubert factors can ever be applied to non-scientific testimony like our cop “experts” give.  The Supreme Court in Kumho Tire expressly “disagree[d] with the Eleventh Circuit’s holding that a trial judge may ask questions of the sort Daubert mentioned only where an expert ‘relies on the application of scientific principles,’ but not where an expert relies on ‘skill- or experience-based observation.’” Kumho Tire, 526 U.S. at 151 (quoting Carmichael v. Samyang Tire, Inc., 131 F.3d 1433, 1435 (11th Cir. 1997)).  As the Court explained in the preceding paragraph of its opinion:

[S]ome of Daubert’s questions can help to evaluate the reliability even of experienced-based testimony.  In certain cases, it will be appropriate for the trial judge to ask, for example, how often an engineering expert’s experience-based methodology has produced erroneous results, or whether such a method is generally accepted in the relevant engineering community.  Likewise, it will at times be useful to ask even of a witness whose expertise is based purely on experience, say, a perfume tester able to distinguish among 140 odors at a sniff, whether his preparation is of a kind that others in the field would recognize as acceptable.

Kumho Tire, 526 U.S. at 151.  The Court then noted that “whether Daubert’s factors are, or are not, reasonable measures of reliability in a particular case is a matter that the law grants the trial judge broad latitude to determine.”  Kumho Tire, 526 U.S. at 153.

There are Ninth Circuit cases applying Kumho Tire, and they’re mixed.  One of the first – United States v. Hankey, 203 F.3d 1160 (9th Cir. 2000) – states a little broadly that “[t]he Daubert factors (peer review, publication, potential error rate, etc.) simply are not applicable to this kind of testimony [from cop “experts”], whose reliability depends heavily on the knowledge and experience of the expert, rather than the methodology or theory behind it.”  Id. at 1169.  But a later cop “expert” case is a little more qualified, quoting Kumho Tire’s caution that “the trial court ‘may consider one or more of the specific factors that Daubert mentioned when doing so will help determine that testimony’s reliability.’”  United States v. Alatorre, 222 F.3d 1098, 1101 (9th Cir. 2000) (quoting Kumho Tire, 526 U.S. at 141, and adding emphasis).  And two later cases held it was error to admit cop “expert” testimony interpreting alleged drug “code words” based on the “expert’s” failure to explain his methodology for arriving at his interpretations of the words in question.  See United States v. Vera, 770 F.3d 1232, 1247-49 (9th Cir. 2015); United States v. Hermanek, 289 F.3d 1076, 1093-96 (9th Cir. 2002).  In Hermanek, the court initially noted that “bare qualifications alone” cannot establish the reliability of expert testimony, id. at 1093-94, and then explained:

Under Rule 702, the proffered expert must establish that reliable principles and methods underlie the particular conclusions offered – here, the interpretation of particular words as referring to cocaine.  As the Supreme Court stated in Kumho, the expert must establish the reliability of the principles and methods employed “to draw a conclusion regarding the particular matter to which the expert testimony was directly relevant.” 526 U.S. at 154, 119 S. Ct. 1167. [The cop “expert”] failed to explain in any detail the knowledge, investigatory facts and evidence he was drawing from.  In United States v. Hankey, by contrast, we approved of a law enforcement expert’s testimony that two witnesses were affiliated with gangs where the expert explained in detail the nature of his personal knowledge and explained the connection between that knowledge and the particular conclusion that the witnesses were gang members.  203 F.3d at 1168-70.  Even if [the cop “expert”] had explained in detail his knowledge of the defendants – such as knowledge they were involved in cocaine trafficking – he would have been required to establish how he applied that knowledge to interpret particular words and phrases used in particular conversations.  (Footnote omitted.)  Without a link between [the cop “expert’s”] knowledge and the particular matter he interpreted, “there is simply too great an analytical gap between the data and the opinion proffered.”  Gen. Elec. Co. v. Joiner, 552 U.S. 136, 146, 118 S. Ct. 512, 139 L. Ed. 2d 508 (1997).

Hermanek, 289 F.3d at 1094-95 (emphasis in original).  Similarly, in Vera, the court explained:

[A]n officer’s qualifications, including his experience with narcotics investigations and intercepted communications, are relevant but not alone sufficient to satisfy Federal Rule of Evidence 702.  Rather, Rule 702 requires district courts to assure that an expert’s methods for interpreting the new terminology are both reliable and adequately explained. [V]ague and generalized explanations are not sufficient; rather, the officer must explain how he applies his knowledge to interpret particular words and phrases used in particular conversations.

Id., 770 F.3d at 1241 (emphasis in original) (citations and internal quotations omitted).

While there are these two examples of reversals on appeal, this is a battle that in most instances will probably have to be won in the district court, because district judges have “considerable leeway,” Kumho Tire, 526 U.S. at 152, and will be reversed only if their rulings are “manifestly erroneous,” Hankey, 203 F.3d at 1167 (quoting Joiner, 522 U.S. at 142).  But this broad discretion also gives you the opportunity to argue the bad cases hold only that it wasn’t an abuse of discretion or manifestly erroneous for the district court to rule as it did, so it does not mean your court has to rule the same way.  (For a discussion of this argument about “not an abuse of discretion” holdings, see the post, “The Case Law They Cite Is About the Abuse of Discretion, Not the Exercise of Discretion,” in the November 2013 link at the right.)