Today the Association of American Law School’s (AALS) Section on Evidence distributed the following announcement to its members:
In a divided decision, the Supreme Court recently concluded that expert testimony about the likely mental state of individuals arrested with drugs in their position is admissible in criminal trials under the Federal Rules of Evidence in Diaz v. United States, 602 U. S. ____ (2024). This decision was sharply contested in its own right, but also drew attention to an area of broader controversy in the law of evidence: the increasing use of "predictive" or "profiling" evidence, by which expert witnesses present testimony suggesting that an individual is more or less likely to have had a particular mental state or behaved in a particular way based on their personal circumstances or characteristics. Scholars who have written about this phenomenon have expressed disquiet about the use of such evidence (and some courts have limited the use of such evidence in edge cases involving particular prejudice or overbroad characterizations), but no consensus has emerged as to the reasons for objecting to predictive evidence or as to how to systematically distinguish between such evidence and other forms of indirect and circumstantial evidence that is routinely admitted. This panel brings together scholars to discuss predictive and profiling evidence from a variety of perspectives. Was the Supreme Court right to find such evidence consistent with the federal rules governing the admissibility of expert evidence? Is such evidence generally consistent with due process and equal protection concerns? Is it generally empirically sound? Do we need new federal rules or common law doctrines to limit the admissibility of some forms of predictive or profiling evidence?
Who can object to a scholarly program on the subject, even if it is hardly new, having been the subject of a multitude of opinions, a number of statutes, and even a previous AALS program decades ago? Hopefully, the courts and the professoriate have made some progress in understanding what has come to be called "framework evidence." Neither would it be fair to criticize a necessarily brief announcement for not defining "predictive or profiling evidence." Presumably, the evidence teachers do not need a definition.
But I was surprised to read my fellow law professors’ sweeping characterization of Diaz v. United States, 144 S.Ct. 1727 (2024), as establishing that "such evidence [is] consistent with the federal rules governing the admissibility of expert evidence" and "that expert testimony about the likely mental state of individuals arrested with drugs in their position [sic?] is admissible in criminal trials under the Federal Rules of Evidence." Although I doubt that the announcement will cause its narrow range of readers to believe that the case stands for more than it does, I do worry that the same kind of language will crop up in undiscerning judicial opinions and commentary on Diaz. Therefore, it may be be worth listing some problematic aspects of the statements.
First, the case plainly held that certain "expert testimony about the likely mental state of individuals arrested with drugs in their position [possession?] is" not "admissible in criminal trials under the Federal Rules of Evidence." Every Justice agreed that no expert can testify that a defendant charged with importing proscribed drugs knew that they were transporting drugs. That would be explicit ultimate-opinion testimony on a criminal defendant's state of mind. (There are cases limiting the Rule 704(b) ban to mental health professionals, but the Court did not consider that possible way to interpret the rule. It stuck with a more literal reading of the text.)
Second, no “predictive or profiling evidence” was introduced in the case, and only one Justice thought it worth discussing. Certainly, Diaz is not a case of a criminal profiler predicting (“inferring” would be more precise) the characteristics of a criminal from the type or manner of the crimes under investigation (or any other such “predictive or profiling evidence”). As the excerpts from the trial transcript reproduced below show, the witness did not claim such expertise; furthermore, the trial judge barred him from stating a belief about the defendant’s knowledge (although one could well think that his testimony made it plain enough what his belief was).
Third, the issue before the Court was not admissibility under the rules of evidence writ large. It was the scope of a single part of a solitary rule. Federal Rule 704(b), which has no counterpart in the rules of most states, declares that no expert witness may "state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense" because "[t]hose matters are for the trier of fact alone." All that the Diaz Court held was that when such an opinion is not stated and is an inference that does not necessarily follow (as a matter of deductive logic) from the witness’s statements, then Rule 704(b) does not preclude its admission. It did not—and could not—have held that the Rule makes it admissible. Cf. David H. Kaye, The Ultimate Opinion Rule and Forensic Science Identification, 60 Jurimetrics J. 75 (2020).
Thus, Diaz should not be read as supporting—or opposing—the use of “predictive or profiling evidence” generally, or even in the subcategory of testimony offered to prove a defendant’s state-of-mind.
More thoughts on the three opinions in the case and how the result fits into the range of possible interpretations of Rule 704(b) will appear in the upcoming supplement to The New Wigmore on Evidence: Expert Evidence § 2.2.3(b) (available online in VitalLaw) and, time permitting, in a further positing about the case here.
Excerpts from Trial Transcript
Mar. 18, 2021
The most pertinent portion of the testimony at issue in Diaz is as follows (with italics added):
BY MR. OLAH [Assistant US Attorney]:
Q. Where do you work?
A. I’m a special agent with Homeland Security Investigations.
Q. And how long have you been with HSI?
A. I’ve been a special agent since 1996. So going on 20 — I believe 28 years.
Q. Were you in law enforcement before joining HSI?
A. Prior to becoming a special agent, I was a U.S. Border Patrol agent. And prior to that, I was a sheriff’s corrections deputy.
***
Q. Have you been involved in drug trafficking investigations as a special agent with HSI?
A. Yes, I have.
Q. Approximately how many such investigations?
A. I’ve been involved in over 500 investigations dealing with distribution of drugs and also the – which would include the importation of drugs.
Q. And can you summarize for the jury the various investigation techniques you’ve used?
A. The techniques I’ve used, I’ve utilized wiretaps, where you actually listen to a drug trafficker talk on the telephone and how they conduct business. I’ve done controlled purchases where I utilized an undercover agent or a cooperating source. And we actually go out on the street and buy the drugs. I’ve spoken with cooperating defendants that have been arrested for drug trafficking related offenses. I’ve talked to cooperating sources that have information related to the distribution of drugs and drug trafficking organizations. I have spoken with other agents that work drug trafficking organizations and have worked on task forces with other agencies such as the Federal Bureau of Investigation, the Drug Enforcement Administration, and local police departments dealing with drug trafficking related crimes.
***
Q. Agent Flood, why are drugs imported into the United States?
MS. IREDALE: Objection, 401.
THE COURT: Overruled.
THE WITNESS: Based upon drugs that – some drugs are manufactured in Mexico and outside the United States. Therefore, they’re brought across the border, into the United States to be sold.
BY MR. OLAH:
***
Q. With respect to vehicles, can you describe the general process of movement from Mexico to wherever it goes?
A. From Mexico, they are packaged. They are put into *** a vehicle. *** I have seen drugs hidden in every area of a vehicle. *** And then they are transported from point A to point B across the border.
Q. And based on your training and experience, are the transporters compensated for their efforts?
A. Yes. It’s a job. It’s to take it from point A to point B.
***
Q. Agent Flood, based on your training and experience, are large quantities of drugs entrusted to drivers that are unaware of those drugs?
MS. IREDALE: Objection. 401, 403.
THE COURT: Overruled.
THE WITNESS: No. In extreme circumstances – actually, in most circumstances, the driver knows they are hired. It’s a business. They are hired to take the drugs from point A to point B.
BY MR. OLAH:
Q. And why aren’t – why don’t they use unknowing couriers, generally?
MS. IREDALE: Objection. 401, 403.
THE COURT: Overruled. You may answer.
THE WITNESS: Generally, it’s a risk of your – your cargo not making it to the new market; not knowing where it’s going; not being able to retrieve it at the ending point, at your point B. So there’s a risk of not delivering your product and, therefore, you’re not going to make any money.
***
Cross Examination
***
Q. So you said that unknowing couriers are very rare.
A. Yes.
***
Q. You work for HSI. Right?
A. Correct.
Q. And you’re aware that your own agency has identified many schemes where drug trafficking organizations use unknowing couriers. Right?
A. I – I know of three schemes that were primarily identified as being possible for an unknowing courier. It doesn’t necessarily mean that they are unknowing couriers. ***
