Police in Massachusetts typically cannot use a drug-sniffing K9 during a routine traffic unless they reasonably suspect that narcotics are present in the vehicle.
If the police dog indicates that drugs are present, officers will have probable cause to search the car or truck. This maybe true even when the dog is mistaken. See Commonwealth v. Pinto, 45 Mass.App.Ct. 790 (1998).
So under what circumstances would a police officer have authority to deploy a drug-sniffing K9 during a roadside stop?
The most obvious scenario is when the motorist shows signs of recent substance use. In Commonwealth v. Perry (2019 WL 4047599), for instance, police were justified in their use of a dog after an erratic driver showed symptoms of being under the influence of stimulants.
In another Massachusetts case, Commonwealth v. Sinforoso, the Supreme Judicial Court held that police properly used a K9 to sniff for narcotics after one of the officers noticed that the stopped vehicle had been altered in a way that caused suspicion. The driver had lowered the vehicle’s gas tank. Ultimately, police found that this was done to create a hidden compartment within the car which could be used to transport illicit drugs.