The traffic stop was made in the town of Hatfield, Mass.
"During the stop, evidence of illegal narcotics led to a request for a State Police K9," the state police said in a statement on the agency's Facebook page. "Trooper David Stucenski and K9 Frankie located 1,250 individual bags of heroin in the vehicle. Four people were taken into custody and charged with narcotics violations."
This post has been updated.