Sam Brasch/CPR News Deuce, an Aurora police dog, is trained to detect marijuana. A recent decision by the Colorado Court of Appeals has left many wondering if Colorado needs police dogs trained for smelling marijuana.

Deuce, a German Shepard with the Aurora Police Department, is sniffing around tables and a barbeque at a picnic area outside a police station. After a few minutes, he sits and fixes his gaze on a plastic trash can.

Deuce’s handler, Sgt. Brandon Samuels, removes a one-pound bag of marijuana he planted for the exercise.

“Guh’ boy!” Samuels said, tossing Deuce a rubber toy.

The Aurora Police Department is one of a number of Colorado law enforcement agencies that trains dogs on marijuana, a legal substance in Colorado. Canines at other agencies in the state ignore pot. A recent court decision has drawn attention to that wide range of policies — and left some wondering if pot-sniffing dogs, like Deuce, are overqualified for their jobs.

Yeah, pot's legal in Colorado. Duece, with @AuroraPD, can still find 1lb bags of it. https://t.co/0rZ5e8mAPE pic.twitter.com/rb3sO6GvKg — Sam Brasch (@samuelbrasch) August 1, 2017

The core of the matter is Kilo, another pot-sniffing dog with the Moffat County Sheriff’s Office. In 2015, officers deployed Kilo to inspect Kevin McKnight’s truck during a vehicle stop. Officers searched the truck following his alert and found a meth pipe containing white residue. Prosecutors used the evidence to convict McKnight on two counts related to drug possession.

The Colorado Court of Appeals recognized a problem. Like Deuce, Kilo can detect cocaine, heroin, ecstasy, methamphetamine and marijuana. Neither dog can indicate which substance it found or the amount.

Since certain amounts of marijuana are legal in Colorado, a three-judge panel ruled Kilo’s sniff an illegal search under state law. As a result, the court said the evidence should not have been admitted in the original trial. The decision overturned McKnight’s conviction.

It also established a new precedent: people in Colorado have a “legitimate expectation of privacy” when they possess something legal, like marijuana. Moffat County officers needed reason to suspect a crime before deploying Kilo.

“This certainly doesn’t prohibit the use of dogs,” explained Jeff Wilson, a Denver-based defense attorney who specializes in cannabis issues. “It just limits the ability of the dog to be a free-standing method of investigation.”

In other words, a signal from a conventionally trained dog alone cannot justify a vehicle search. Deputies must first observe something else, like slurred speech or the sight of drugs.

So what does all that mean for dogs like Deuce? The dogs put prosecutors at risk of having evidence suppressed, even if that evidence has nothing to do with marijuana. That’s why some have speculated dogs might have to be retrained or retired. Samuels, who supervises Aurora’s K9 unit, said that’s not the case.

Sam Brasch/CPR News Sgt. Brandon Samuels of the Aurora Police Department and his canine companion, Deuce.

For one, Samuels thinks the McKnight ruling fits with a 2016 Colorado Supreme Court decision. That case established a standard known as “odor-plus.” It means if a dog can detect pot, its alert can only be part of the reason for a vehicle search. The Aurora Police Department strictly follows that standard, Samuels said.

“Especially since marijuana was legalized, we have not and would not use solely a dog alert as justification to search a vehicle.”

The department follows that standard to uphold the Fourth Amendment, which protects people in the U.S. from unreasonable search and seizures. He has heard fears that police use dogs to justify a search when citizens won’t consent.

“People don’t need to worry about having their basic freedoms violated. We are not going to search people just to search people,” he said.

As for retraining Deuce, Samuels does not think it would work. K9 officers in Seattle, where marijuana is also legal, claim they successfully taught their dogs to ignore pot. Samuels is skeptical. He thinks once a dog learns a scent, it cannot forget it.

Retirement is also out of the question for Deuce. At three-years-old, Samuels hopes to get another 8 to 10 years of work from him.

“If we were to retire him, we would be losing a very valuable asset that is very well trained,” he said.

Other police departments in Colorado have phased out pot-sniffing dogs. All four of the canines working in the Loveland Police Department ignore pot, according to Sgt. Steve Colburn.

That’s no accident. After Colorado voted to legalize marijuana in 2012, the Loveland was unsure how courts would rule on evidence turned up by its dogs. The department started to replace retiring dogs with ones with no nose for marijuana. The Greeley Police Department has done the same. The Weld County Sheriff’s Office is also in the process of replacing its dogs.

The Colorado State Patrol has changed directions on the issue. After Colorado legalized recreational marijuana, the agency decided to purchase canines not sensitive to the drug. Their calculus changed after the “odor-plus” ruling in 2016. Now, the agency trains some dogs on marijuana, according to State Patrol Sgt. Rob Madden.

Those dogs, along with others at local police departments, help combat black-market marijuana in Colorado.

Since the McKnight decision, Denver has planned to start using some dogs not trained to detect marijuana. Meanwhile, police in Pueblo have no plans to phase out their cannabis-capable canines. At the time of publication, police in Fort Collins, Thornton and Colorado Springs had not commented on their dog training policies and if they would change.

Aurora plans to keep training its dogs on marijuana, for now.

“When we get new dogs, my personal recommendation will be that we do not train them on marijuana whatsoever and that they are never exposed to it,” Samuels said.

He's not quite ready to make that call though. The Colorado Attorney General’s Office is reviewing whether to appeal the McKnight decision to the Colorado Supreme Court. Without final clarity, Aurora police probably will not decide the future of its pot-sniffing companions.