PHOENIX — The smell of marijuana is no longer enough in Arizona for police to get a warrant and come busting down the door, the state Court of Appeals has ruled.

In a split decision, the judges acknowledged that the odor of the plant, whether fresh or freshly smoked, was enough to provide police with probable cause that a crime was taking place. And that provided the basis to go to a judge to seek permission to enter where the smell was coming from.

But Judge Peter Eckerstrom, writing for the majority, said that changed in 2010 when voters approved the Arizona Medical Marijuana Act.

“Medical marijuana use pursuant to AMMA is lawful under Arizona law,” he wrote. “Therefore its scent alone does not disclose whether a crime has occurred.”

Put simply, Eckerstrom wrote, the smell of marijuana, absent other evidence, does not provide the constitutional basis for a search. Instead, the court set up what it called an “odor-plus” standard.

The ruling is a setback for police and prosecutors who until now have not needed additional justification and argued to the court to uphold the warrant.

“Were we to adopt the state’s suggestion that scent alone furnishes probable cause of a crime, medical marijuana patients would become second-class citizens, losing their rights to privacy and security, including privacy within their own homes,” Eckerstrom wrote.

David Euchner, an assistant Pima County public defender who argued the case, was cheered by the ruling. But he warned the decision is not an absolute escape clause for those who possess marijuana illegally.

He said there clearly are situations where odor alone can provide the basis for a search, such as when someone is inhaling something in a public place. And Euchner said what someone tells police also could create sufficient probable cause for a warrant.

Amelia Cramer, chief deputy Pima County attorney, agreed that the ruling is far from a blanket ban on police using the smell of marijuana to build a case against someone and get a warrant. But she said it is clear that odor alone won’t provide the basis for searches unless the ruling is overturned by the Arizona Supreme Court.

The case involves three police officers, one from South Tucson and two from Tucson, who said there was an “overpowering” odor of fresh marijuana coming from a warehouse in a four-unit complex. After obtaining a warrant based only on the smell, police entered and discovered 357 plants and 53 pounds of cultivated marijuana.

There also was evidence that the building served as a residence and items indicating a young child lived there.

Ronald J. Sisco II, who was an occupant, was subsequently arrested. His bid to have the search warrant quashed was rejected by a trial judge and he was found guilty.

Eckerstrom said a search warrant requires “probable cause.” And that, he said, requires that an officer show he or she knows facts that would conclude the items sought are connected with criminal activity.

More to the point, the judge said, a warrant cannot rely on behavior that might as equally be legal as illegal. And the 2010 vote changed all that.

“The possession of marijuana is not illegal per se, and therefore its scent alone does not disclose whether a crime has occurred,” Eckerstrom wrote.

The law allows individuals with a doctor’s recommendation to obtain up to 2½ ounces of the drug every two weeks. It also allows dispensaries to grow an unspecified number of marijuana plants at off-site facilities. And caregivers can cultivate up to 60 plants.

However, the smell of marijuana could indicate someone is possessing it illegally.

“However, a reasonable, prudent and cautious person could not, in the absence of further information, form a well-founded belief that a criminal offense was committed,” the judge said.

Eckerstrom acknowledged the ruling may catch police off guard, as they have operated for years under the premise that marijuana is illegal under all circumstances.

“Law enforcement officers may therefore have understandably developed practices in accord with that now-outdated assumption,” he said.

Euchner said the ruling — and the new odor-plus standard — makes sense.

“It’s just like if they smell alcohol on a driver’s breath,” he said — that could be evidence someone has been driving drunk.

“It’s something an officer can ask more questions about,” he said. “But they can’t just arrest just because they smell alcohol on the breath.”

Euchner said a police officer who comes into contact with someone who smells of marijuana is free to ask questions, including whether the person has a legal right to possess the drug.

“The person may choose not to answer them,” he said.

Euchner said the new limits also are true even in situations where police might not normally need a warrant, such as when they’ve pulled over a vehicle.

Still, there are limits to the reach of the ruling. For example, Eckerstrom pointed out that the 2010 law does not authorize the use of marijuana in public.

“Therefore its smoke emanating from a public area would still provide probable cause for arrest and reasonable suspicion for an investigatory detention,” the judge said.

The ruling was not unanimous, with appellate Judge Philip Espinosa saying his colleagues were guilty of “innovative reasoning — and not in a good way. And he chided them for raising “alarmist fears” about police and SWAT teams invading homes of citizens based simply on the smell of marijuana.

He said the fact that the police could smell the marijuana from outside the building 60 feet away gave police reason to believe this wasn’t just some individual with 2½ ounces of marijuana. And he said the building in the case had “none of the hallmarks” of a state-approved and regulated cultivation facility.

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