Here’s a scenario: Let’s say police one night pull over a pickup truck, and let’s say that a narcotics dog almost immediately gives an alert that it smells drugs when it approaches the vehicle.
There’s a twist, though. In addition to being trained to sniff for methamphetamine, cocaine, heroin and ecstasy, the dog is also trained to give the same alert when it smells marijuana — even though Colorado law doesn’t make possession of marijuana inherently criminal.
Now, here’s a question: Do police have enough evidence of a crime to search that truck?
For the six years since Colorado voters approved marijuana legalization, state and local law enforcement agencies have hedged on that question. Departments across the state have retired their not-that-old K-9s brought up to smell marijuana as a crime and replaced them with sprightly new dogs that are cool with cannabis. That makes the new dogs’ bark beyond reproach in drug cases.
But it’s never been settled law that this transition had to occur in the first place. On Wednesday, the Colorado Supreme Court will hear arguments about whether an alert from a marijuana-sniffing dog is alone enough to justify a search. In doing so, it will return to the bigger question the state’s highest court has visited time and again since 2012: What exactly did it mean for Colorado voters to “legalize” marijuana?

What is the Supreme Court deciding?
That scenario above is a slimmed-down version of the real-life events that will come before the Supreme Court on Wednesday.
In 2015, police officers in Craig pulled over a truck driven by a guy named Kevin McKnight. McKnight’s passenger was someone prosecutors describe as “a known methamphetamine user,” and the truck had been seen leaving a house where police had several weeks prior served a search warrant and found drugs. Prosecutors argue those facts gave police a good reason to be suspicious.
After the dog — named Kilo — gave an alert, police searched the truck and found a pipe with meth residue in it underneath a seat. McKnight was convicted of possession of a controlled substance and possession of drug paraphernalia, and he was sentenced to 30 days in jail and two years on probation.
McKnight appealed, though, saying that the pipe should have never been allowed into evidence because it came from an illegal search. Because Kilo had been trained to sniff for marijuana along with other drugs and because Kilo would give the same alert no matter what drug was found, McKnight said there was no way for police to know if Kilo had detected something that was legal or illegal.
Three judges of the Colorado Court of Appeals — each writing their own opinion — tended to agree and threw out McKnight’s conviction. But prosecutors argued that the ruling completely misunderstood marijuana legalization and appealed to the state Supreme Court.

Legalization doesn’t mean marijuana is legal
The Colorado Attorney General’s Office, which is representing prosecutors’ side in the case, raised a host of arguments in its appeal, but many came back to this: Even though Colorado voters passed marijuana legalization, that doesn’t mean pot is legal here.
Instead, in what has now become a well-worn (and often successful) argument at the state Supreme Court, the attorney general’s office says that voters in 2012 actually kept marijuana illegal except for a few exemptions in the law — such as possession of an ounce or less by a person 21 years old or older. That means, according to the attorney general’s office, almost all the architecture around marijuana prohibition remains in force. And that includes alerts from drug-sniffing dogs.
“Amendment 64 does not preclude otherwise legal searches or change pre-existing law concerning such searches,” the attorney general’s office writes in its brief, referencing the recreational marijuana ballot initiative in Colorado.
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McKnight’s attorneys vehemently oppose this view.
“If this Court adopts the prosecution’s position, it will result in innumerable invasions of privacy of law-abiding Coloradans and visitors to Colorado,” they write in their brief.
But the Colorado Supreme Court has often decided in recent years against people arguing for a broader view of legalization.
Take, for instance, the case of Brandon Coats, a medical marijuana patient the Supreme Court said was legally fired for off-the-clock cannabis use. Marijuana is still illegal under federal law, the court ruled, so it can’t be considered fully legal here for employment purposes.
The state Supreme Court has previously let stand a ruling that people on probation have no right to use marijuana. Despite legalization, the court ruled in 2016 that “the odor of marijuana can support an inference that a crime is ongoing.”
It’s even already passed judgment on marijuana-sniffing dogs. In that 2016 ruling and last year, too, the state Supreme Court ruled that a marijuana-trained drug dog’s alert can, in combination with other factors, be “considered under the totality of the circumstances” in determining whether there’s enough evidence to justify a search.
In each of those cases, the court ruled that the dog’s alerts, “suggested that illegal drugs were present in the vehicle.”
The question now is whether a dog’s alert can be the only thing suggesting illegal drugs are present.
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