The Effect of Legal Hemp on Drug Dog Sniffs (Part I)

Hemp and hemp products are now legal under state and federal law. Hemp is the same plant as marijuana and contains the same chemical compounds, though in different concentrations. Could a drug dog trained to detect marijuana alert on legal hemp? If so, does that impact whether a dog sniff is a search under the Fourth Amendment? And does it mean that a drug dog’s alert no longer provides probable cause to search a vehicle? This two-part series tackles those questions.

A dog could alert on legal hemp. So says the State Bureau of Investigation in this memo: “Police narcotics [K-9s] cannot tell the difference between hemp and marijuana because the [K-9s] are trained to detect THC which is present in both plants.” Other sources reach the same conclusion. See, e.g., Bill Bush, Is it hemp or is it pot? Drug dogs can’t say, Columbus Dispatch (Aug. 12, 2019) (reporting that “[b]ecause marijuana and hemp are both from the cannabis plant and smell identical, dogs can’t tell the difference, so both the Ohio Highway Patrol and the Columbus Division of Police are suspending marijuana-detection training for new police dogs to uncomplicate probable cause issues in court” and noting that the Columbus City Attorney has directed that “a vehicle may not be searched solely because a K-9 trained to alert to marijuana, alerted to the vehicle”); Jennifer Kendall, Legal hemp could affect Texas’ drug detection dogs, Fox 7 Austin (July 3, 2019) (“The Texas District and County Attorney’s Association said drug dogs are not qualified to distinguish between legal hemp and illegal marijuana.”).

My understanding is that many new dogs are being trained to alert only to cocaine, methamphetamine, and other hard drugs. Because they are not being trained to alert on marijuana, these dogs presumably won’t alert on hemp, and the analysis in this post won’t apply to these dogs. This post focuses on legacy dogs who are trained to alert on marijuana and so may alert on hemp.

Is the sniff a “search”? Until recently it was clear that most drug dog sniffs weren’t searches for purposes of the Fourth Amendment. In Illinois v. Caballes, 543 U.S. 405 (2005), the Supreme Court held that “any interest in possessing contraband cannot be deemed legitimate, and thus, governmental conduct that only reveals the possession of contraband” doesn’t infringe on a reasonable expectation of privacy. Prior to the legalization of hemp, drug dogs only alerted on contraband, meaning most drug dog sniffs were not searches and so did not require probable cause or any other legal justification.

I keep saying that most dog sniffs were not searches because in Florida v. Jardines, 569 U.S. 1 (2013), the Supreme Court held that taking a drug dog to the front door of a home is a search under the trespass theory of the Fourth Amendment. But drug dogs are most frequently used on cars during traffic stops and under Caballes, a dog may sniff a stopped car without any level of individualized suspicion, so long as the sniff does not prolong the stop in violation of Rodriguez v. United States, 575 U.S. 348 (2015).

The reasoning in Caballes has always struck me as odd. Courts normally use the reasonable expectation of privacy analysis to determine whether a person has a constitutionally significant interest in a place or container – like a house, car, bag, or phone. The analysis generally doesn’t focus on the contents of the place or container. The reasonable expectation of privacy framework was born in Katz v. United States, 389 U.S. 347 (1967), where the Supreme Court ruled that a person has a reasonable expectation of privacy in a telephone booth, regardless of what he or she discusses therein.

Whatever the merits of Caballes, there’s a reasonable argument that it doesn’t apply to drug dogs that may alert upon smelling non-contraband items like hemp, because a person may have a reasonable expectation of privacy in non-contraband. Thus, in State v. Walters, __ N.C. App. __, 881 S.E.2d 730 (2022), the defendant argued that “[b]ecause the dogs signal to THC, which is present in both marijuana and hemp, and because Defendant now has a legitimate privacy interest in hemp . . . the use of drug-detecting dogs” is no longer supported by Caballes.

The Walters court disposed of the case on the basis that methamphetamine was found in the vehicle search that followed the dog’s alert, and “Defendant did not have a ‘legitimate privacy interest’ in his methamphetamine.” See also State v. Teague, __ N.C. App. __, 879 S.E.2d 881 (2022) (concluding without extensive discussion that a dog sniff was not a search despite the legalization of hemp). But it seems to me that Caballes turns on what a dog is able to detect, not what it actually detects in a particular instance. If a dog is able to detect non-contraband, then a sniff is a search, regardless of what, if anything, the dog or subsequent human searchers eventually find. Put differently, the sniff either was or wasn’t a search when it took place. The Walters approach makes the status of the sniff depend on the results of the investigation – the sniff is not a search if drugs are found, but it is a search if nothing or only hemp is found. That puts officers in an impossible position. An officer deciding whether to deploy his or her dog would have no way to know whether having the dog sniff a vehicle was a search that requires legal justification until after the sniff and any subsequent search of the vehicle was completed.

Even if Caballes doesn’t apply to sniffs by legacy drug dogs, it doesn’t necessarily follow that a sniff is a search. It is not a search for a police officer to smell the odor of marijuana emanating from a vehicle on a public street. The odor is exposed to the public. This is the plain smell doctrine, and while most of our cases in this area focus on the sufficiency of the odor to justify a subsequent search of the vehicle, courts have never suggested that the officer is conducting a Fourth Amendment search simply by smelling the air near a vehicle. See, e.g., State v. Greenwood, 301 N.C. 705 (1981); State v. Smith, 192 N.C. App. 690 (2008) (“When an officer detects the odor of marijuana emanating from a vehicle, probable cause exists for a warrantless search of the vehicle for marijuana.”); State v. Armstrong, 236 N.C. App. 130 (2014) (“[O]fficers had probable cause to search [a vehicle] based upon the odor of marijuana emanating from the vehicle.”). The Fourth Circuit addressed the issue in United States v. Mitchell, 720 Fed. Appx. 146 (4th Cir. 2018) (unpublished), where it held that officers who sniffed at the exterior of an apartment “[did] no violence to the Fourth Amendment by gathering evidence in [a] public place[] using their unenhanced senses.”

Arguably the same principle should apply to drug dogs. Odors coming from a vehicle may be in “plain smell” of all who pass by, even those who have more sensitive noses than humans do. The vehicle’s occupants may therefore have no reasonable expectation of privacy in those odors. Some support for this argument may be found in the pre-Caballes case of United States v. Place, 462 U.S. 696 (1983), where the Supreme Court ruled that a dog sniff was not a search, in part because it was “much less intrusive than a typical search” and did not even require opening the luggage that was the focus of the case.

On the other hand, because drug dogs can smell much more effectively than humans can, perhaps having a drug dog sniff a car is like using a thermal imager on a home. In Kyllo v. United States, 533 U.S. 27 (2001), the Supreme Court ruled that a Fourth Amendment search takes place when “the Government uses a device that is not in general public use, to explore details of the home that would previously have been unknowable without physical intrusion.”

Whether a drug dog sniff is a search was debated in State v. McKnight, 446 P.3d 397 (Colo. 2019). The case arose after Colorado legalized marijuana. A majority of the court concluded that Caballes didn’t apply because drug dogs could now detect non-contraband. Citing Kyllo, the majority concluded that “a sniff from a drug-detection dog that is trained to alert to marijuana constitutes a search under . . . the Colorado Constitution because that sniff can detect lawful activity, namely the legal possession of up to one ounce of marijuana by adults.” Two dissenting justices argued for the applicability of the plain smell doctrine, writing that a driver has no “reasonable expectation of privacy in the odors that escape from his car and become part of the public airspace,” and contending that drug dogs aren’t like the thermal imagers at issue in Kyllo.

So, are legacy drug dog sniffs now searches? If I were representing the State, I would feel comfortable arguing that they are not. Walters is the North Carolina case most closely on point and it seems to say that Caballes remains the proper framework in most cases. Plus I would have the plain smell argument in my back pocket. But if I were on the defense side, I would feel comfortable arguing that the logic of Caballes doesn’t apply to dogs that can smell hemp, and that Kyllo defeats the plain smell theory. Walters gives the State the upper hand right now, but I don’t expect it to be the last word on this.

Come back next week for Part II of this series, where I’ll try to sort out whether a legacy drug dog’s alert provides probable cause to search a vehicle given that the alert may be based on the presence of legal hemp. In the meantime, if you want to get up to speed on other issues involving cannabis, hemp, and related matters, my colleague Phil Dixon is on top of it. You can search for his posts on this blog, or if you want a suggestion about where to start, this cannabis update post is a great point of entry.