The case arose from a drug surveillance operation where Boston police Officer Matthew Pieroway observed Jose Arias commit a civil traffic infraction on March 27, 2019. Arias pulled his SUV to the right side of a line of stopped vehicles, passed them without stopping at a stop sign, and took a left turn in front of the line. Pieroway was conducting surveillance in an unmarked vehicle but did not attempt to stop Arias or call for a marked cruiser.

The next day at 3:27 p.m., when Pieroway again spotted Arias during surveillance, he radioed for a marked cruiser to stop the vehicle, stating over police radio he was "looking to stop a vehicle for [a] drug investigation." The subsequent stop yielded cocaine on Arias's person and in his vehicle.

Justice Dalila Dewar wrote that while police may stop vehicles for observed traffic violations, such stops must be conducted reasonably, and the 24-hour delay here was unreasonable. "An observed civil traffic infraction cannot hang over a suspect indefinitely until a time at which he has engaged in some other suspicious activity that officers believe warrants a pretextual stop," Dewar wrote.

The court emphasized that "the passage of time after such a violation increases the possibility of arbitrary police conduct." The opinion explained that civil traffic infractions are "uniquely suited to manipulation and misuse" because "very few drivers can traverse any appreciable distance without violating some traffic regulation."

The court rejected the Commonwealth's safety justifications for the delay, noting that the record did not explain why Pieroway didn't call for a marked cruiser immediately, as was his regular practice. When pressed for an explanation, the officer gave only a one-word reply of "safety."

The case reached the SJC after Superior Court Judge Peter B. Krupp denied Arias's motion to suppress evidence from the traffic stop. Judge Krupp had noted "the lack of reported cases in Massachusetts addressing whether a motor vehicle stop may be based on a traffic violation witnessed the previous day." The defendant was initially charged with trafficking 200 or more grams of cocaine, but after a mistrial, the Commonwealth reduced the charge and Arias was convicted of trafficking eighteen to thirty-six grams of cocaine.

The unanimous decision reversed the denial of Arias's suppression motion and vacated his conviction.