On June 20, 2024, the United States Supreme Court held that federal prosecutors in drug cases can present expert witness testimony about whether most drug couriers are aware that they are transporting illegal drugs. The case is Diaz v. United States, No. 23-14, slip op. (U.S. June 20, 2024). Justice Gorsuch called the permitted expert testimony “a powerful new tool in [the government’s] pocket.” Id., slip op at 1 (Gorsuch, J., dissenting).
Before Diaz, the federal courts of appeal were split about whether this type of testimony was admissible. In the Fifth Circuit, which covers federal courts in Texas, Louisiana, and Mississippi, this type of testimony was not permitted for more than two decades. See United States v. Gutierrez-Farias, 294 F.3d 657, 663 (5th Cir. 2002). Indeed, the Fifth Circuit recently reiterated that an expert witness cannot testify that drug couriers “usually” know that they are transporting illegal drugs. See United States v. Lara, 23 F.4th 459, 476-77 (5th Cir. 2022). Diaz changed that. This article will discuss the practical effects of Diaz on federal drug trials in Texas.
BACKGROUND: “BLIND MULES.”
In drug slang, a “mule” is someone who does nothing more than transporting drugs from one place to another, like a pack mule. When a drug mule is charged in a federal drug case, they often claim that they did not know they were carrying drugs.
Maybe they were offered money to take a backpack from one person to another, and they claim they never looked in the backpack, so they did not know what was in it. Maybe they are offered money to drive a car from one place to another, and they claim they never looked in the trunk or in a secret compartment where the drugs were located, so they did not know they were driving drugs from one place to another.
In order to prove a mule guilty, the Government must prove that the mule “knowingly” transported drugs. See 21 U.S.C. §§ 952 and 960. A person who truly has no idea that he is transporting illegal drugs is therefore not guilty of a federal drug crime. The claim that a mule did not know he was actually transporting drugs is called the “blind mule” defense.
There are many ways in which the Government can potentially prove that a mule knew he was transporting drugs. For example, there are sometimes text or direct messages in obvious code language directing a person to pick up a package and take it to another person. An obvious message in code might go something like this: “I need you to go pick up five roosters and bring them to The Mechanic. He will give you 30 for them.” Then, surveillance sees the recipient of the message arrive at The Mechanic’s shop with a large bag, and the contents turn out to be five kilos of illegal drugs. That is pretty good evidence that the mule was not blind.
At other times, though, there may be less evidence to show how the mule actually knew he was transporting drugs. This is where the expert testimony at issue in Diaz comes in.
The Supreme Court’s Diaz Opinion.
In Diaz, a woman who was an American citizen was driving from Mexico into California. At a port of entry, a border patrol agent asked her to roll down her rear driver’s side window. She said that the window was manual, so the agent tried to roll it down himself. The agent felt some resistance when he tried to roll down the window and heard a “crunch-like sound.” The border patrol agent knew from experience that drugs can be smuggled in the door panels of cars, so he used a tool called a “buster” to determine whether the door was abnormally dense. It was, so he called for a drug-sniffing dog and sent the car through an X-ray machine. The agents discovered 56 packages of methamphetamine, weighing over 54 pounds, hidden in the door panels and under the carpet in the trunk. The estimated value was over $368,000.00.
Ms. Diaz claimed that she had no idea that drugs were hidden in the car. She said that she had been in Mexico visiting her boyfriend and that the car was his.
At trial, a Homeland Security Investigations agent testified that, “in most circumstances, the driver knows they are hired…to take the drugs from point A to point B.” Diaz, slip op. at 3. The agent reasoned that drug traffickers are normally not willing to take the risk that the drugs would not arrive at the intended destination, and even if they did, they would not want to risk having to recover the drugs without detection. Essentially, his testimony was that drug trafficking organizations will rarely put hundreds of thousands of dollars worth of drugs in the control of someone they do not trust. He did acknowledge, however, that drug trafficking organizations sometimes do use blind mules.
Ms. Diaz was found guilty. On appeal, she argued that the trial court committed a legal error by allowing the Homeland Security Investigations agent to testify as an expert witness that most mules know they are transporting drugs.
The actual legal issue in Diaz was not about what is fair or the best policy. It was about interpreting Rule 704 of the Federal Rules of Evidence. Rule 704(b) states:
In a criminal case, an expert witness must not 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. Those matters are for the [jury] alone.
Fed. R. Evid 704(b).
As noted above, in order to prove someone guilty of drug trafficking, the Government must prove that the defendant “knowingly” participated. This means that the person must know that they are transporting illegal drugs. The question in Diaz, was, therefore, whether testimony that most mules know they are transporting drugs is an “opinion about whether the defendant did or did not have a mental state…that constitutes an element of the crime.” If it was, Rule 704(b) says that it is inadmissible.
The Supreme Court held that the expert testimony was admissible, reasoning as follows:
Rule 704(b) applies only to opinions about the defendant. Because Agent Flood did not express an opinion about whether Diaz herself knowingly transported methamphetamine, his testimony did not violate Rule 704(b).
* * * *
Agent Flood instead testified about the knowledge of most drug couriers….That opinion does not necessarily describe Diaz’s mental state. After all, Diaz may or may not be like most drug couriers.
Diaz, slip op. at 7.
On the other hand, Diaz held that an opinion about “all people” in the defendant’s position, rather than “most,” would include the defendant. See id. Such an opinion would therefore be inadmissible under Rule 704(b).
The Impact of Diaz on Federal Drug Trials in Texas.
After Diaz, federal prosecutors in Texas will be able to present expert testimony that most people who are transporting illegal drugs know that they are doing so. Before Diaz, they could not. As a practical matter, how much will this affect a defendant’s chances of a not guilty verdict? In my opinion, if the defense lawyer is skilled, knows what they are doing, and does their homework, probably not much.
First, even if federal prosecutors had not been able to call a witness to say that most drug traffickers know what they are doing, they certainly made that argument to the jury in closing arguments. They would argue pretty much the same thing that the expert witness could say—that drug trafficking organizations will not trust valuable assets to someone they do not know they can trust. I doubt that having a witness say that will make much of a difference in practice.
On the other hand, an expert witness who expresses this opinion will be subject to some potentially powerful cross-examination. As a so-called “expert,” for example, the witness would be expected to know that, despite the expert’s seeming logic, the use of “blind mules” does happen. The Government’s expert witness in the Diaz case admitted as much. See Diaz, slip op. at 4. Indeed, a drug smuggling ring in El Paso relied on blind mules, lookouts, GPS trackers, and a locksmith with access to Ford’s key database. See Order Accepting Guilty Plea, United States v. Chavez, No. 3:12-CR-318 (W.D. Tex. May 25, 2012).
There are good reasons that drug traffickers might prefer blind mules. First, drug traffickers do not need to pay blind mules, because they do not know they are working. Second, someone who is unknowingly transporting valuable drugs is unlikely to steal them. Third, someone who does not know they are transporting drugs is less likely to appear nervous at a border check point. Fourth, if a blind mule is caught, the blind mule will not be able to snitch on the others who are involved.[1]
The fact that blind mules do occur, and the reasons why they can be attractive to drug trafficking organizations, can be more powerful and persuasive during a trial if the Government’s own expert witness must acknowledge them during cross-examination. Making this work with an adverse Government witness, however, takes skill and preparation.
The Government’s use of this kind of expert witness also creates potential opportunities for discovery of information in the Government’s possession about the existence and prevalence of blind mules. For example, the U.S. Attorney’s Office for the Southern District of California has created packets of information on investigations into blind-mule schemes that it provides to defense lawyers in such cases.[2]
As a result of Diaz, there have been significant efforts to document the use of blind mules. In cases where a defendant’s knowledge of illegal drugs is an issue, federal criminal defense lawyers should be aware of this documentation and should know how to use it.
CONCLUSION.
Diaz did give federal prosecutors in Texas a new tool—expert witnesses who can testify that most drug couriers know they are transporting drugs. The use of this tool, however, opens a lot of opportunities for a skilled and experienced federal criminal defense lawyer to make their defense even more effective and persuasive.
If you or a loved one has been charged with a federal drug crime, you should consult with an experienced federal criminal defense lawyer who has particular expertise in drug cases. Federal drug cases are way too serious to trust to anyone else.
[1] See Diaz, Amicus Brief of National Association of Federal Defenders at 13-14.
[2] See Diaz, Amicus Brief of National Association of Federal Defenders at 11.