Colorado police can no longer deploy drug-sniffing dogs to search vehicles or homes without probable cause, according to a new ruling by the state Supreme Court. The court's chief justice dissented with the majority opinion, however, arguing that the federal government could use this decision as ammunition to overturn the state's cannabis legalization law.

The original case began in 2015, when Kevin McKnight was pulled over in Craig, Colorado, for allegedly failing to signal a turn. Cpl. Bryan Gonzales, the officer making the traffic stop, “recognized the passenger as someone who had used methamphetamine 'at some point in the past,' but he wasn't sure how recently,” according to Reason. Gonzales called for a drug-sniffing dog named Kilo, who barked to indicate that he smelled drugs in the vehicle. 

Using Kilo's bark as justification, cops searched the vehicle and discovered methamphetamine and drug paraphernalia. McKnight was arrested for possession, but challenged his conviction in court. In 2017, a state appeals court decided the case in favor of the defendant, ruling that deploying a drug-sniffing dog constitutes a search, which requires that police have probable cause to believe that a crime has been committed.

Earlier this week, the state Supreme Court ruled 4-3 to uphold the lower court's decision, reversing the criminal charges against McKnight. “The dog’s sniff arguably intrudes on a person’s reasonable expectation of privacy in lawful activity,” Justice William Hood wrote in the ruling, according to The Colorado Sun. “If so, that intrusion must be justified by some degree of particularized suspicion of criminal activity.”

The Colorado court's decision runs contrary to that of the U.S. Supreme Court, which has ruled that a sniff by a drug-detecting dog is not a search on its own, but does provide probable cause for a vehicle search. In the majority ruling, the justices wrote that “an exploratory sniff of a car from a dog trained to alert to a substance that may be lawfully possessed violates a person's reasonable expectation of privacy in lawfully possessing that item,” Reason reports. “Because there was no way to know whether Kilo was alerting to lawful marijuana or unlawful contraband, Kilo's sniff violated McKnight's reasonable expectation of privacy. Therefore, under state law, Kilo's sniff was a search that had to be constitutionally justified."

Chief Justice Nathan Coats dissented strongly with the court's majority opinion, calling the decision “deeply flawed” and “revisionist.” In his dissent, Coats wrote that he is “particularly concerned that... the majority unwittingly exposes not only the marijuana initiative itself but even the state’s constitutional Bill of Rights to a much greater risk of federal preemption than would previously have been the case.”

The “federal preemption” Coats is referring to means that whenever federal and state law disagree, federal law overrules state law. The Chief Justice has raised concerns that the court's ruling could limit how federal law enforcement conduct searches in the Centennial State, which might prompt the U.S. government to challenge Colorado's entire adult-use law via a preemption case.

Sam Kamin, cannabis law professor at the University of Denver, doesn't believe that the ramifications of the ruling are quite so dire. “I don’t think this creates any obstacle to the federal government enforcing federal law,” he said to the Sun. “The states are under no obligation to enforce federal law.”