The Supreme Judicial Court ruled today that a police officer who stopped David Privette not long after the robbery of a gas station one night in 2018 had enough probable cause to conclude he was a suspect even before he found him packing a gun and several hundred dollars in cash, and so prosecutors can bring him to trial.

It's a similar outcome to the one Privette got in 2021 when the Massachusetts Appeals Court considered his case. But in its ruling today, the state's highest court also tightened up the rules by which officers who may not have direct knowledge of why a particular person is being sought can still arrest him or her during a manhunt.

The case focuses on events after a Shell station on Morrissey Boulevard was robbed at gunpoint shortly after 3:30 a.m. on Aug. 12, 2018 and two BPD officers, driving in separate cruisers, came upon Privette as he walked in the rain down Ashland Street in Clam Point, a small, normally quiet area just off Morrissey Boulevard not far from the station.

The SJC concluded that the officer who first "seized" Privette by announcing "Boston Police" and "Show me your hands" had reasonable suspicion to do so: Radio traffic on the Dorchester police channel before the encounter had been filling with details about the suspect in the gas-station robbery, including the fact that, like Privette, he had a beard, that Privette was not far from the gas station and that while Clam Point is not a high-crime area, the fact that Privette was walking in the rain on what would normally be a deserted Clam Point street in the middle of the night was suspicious.

Privette's attorney argued that because he was found so close to the gas station should argue against arrest, on the grounds that nobody who just robbed a place would stick around nearby, but the court said this was mitigated by the fact that his reported direction of flight after the robbery - and the fact that one of the officers, a Clam Point native, knew about a large hole in a fence behind the gas station that any sensible robber would take.

But that part of the ruling is near identical to the reasons the appeals court gave in 2021 for rejecting pleas to rule the initial "seizure" and subsequent recovery of a gun and money illegal. On appeal to the SJC, Privette's attorney raised a new question, related to "the collective knowledge doctrine" by which officers can arrest somebody even if they don't have much or any first-hand information about why a particular person might be a suspect.

That's not much of an issue in arrests for what are known as "vertical" situations, for example, a commanding officer directs a patrol officer to arrest a particular person based on a series of facts and determinations that the patrol officer might not be fully privy to - or when a police department in one city asks a department in another to arrest somebody - the court said.

But Privette's arrest involved "horizontal collective knowledge," in which two or more officers look to arrest somebody, during a manhunt, say, based on bits of information each might have during an active search:

"The horizontal knowledge doctrine, by contrast, permits the aggregation of information known to multiple officers; no one officer need have sufficient information to support probable cause or reasonable suspicion. Instead, "a number of individual law enforcement officers have pieces of the probable cause puzzle" that are aggregated to meet the threshold. See Chavez, 534 F.3d at 1345. Under the horizontal collective knowledge doctrine, officers are not acting at the direction of another, as they would be under the vertical collective knowledge doctrine."

There's a risk to a person's rights under the Massachusetts constitution in that, the justices reasoned: A cop engaged in a manhunt might arrest somebody with no real probable cause or reasonable suspicion on the hopes that other officers on the case might have information that would be legally enough for an arrest - or that a group of officers could arrest somebody and then try to dig up the sort of information needed to charge the person after the fact.

To guard against that, the court today set down guidelines for such manhunts.

"Where there is no directive or instruction from a superior officer, in order to aggregate officers' knowledge for use in the determination of reasonable suspicion without running afoul of art. 14, the officers must be involved in a joint investigation, with a mutual purpose and objective, and must be in close and continuous communication with each other about that objective."

This, they said, would help minimize potential reasonable-search issues while still letting officers find a criminal who poses a potential threat to the public. And that's what happened with the two officers who came upon Privette at nearly the same time, the court concluded:

Dwan and Doherty were actively working on apprehending the suspect involved in the armed robbery; indeed, they arrived at the scene of the stop contemporaneously. The two officers jointly conducted a patfrisk of the defendant's person and backpack. This is more than sufficient to be considered a joint investigation for a shared, mutual objective.

In contrast, they said, information gathered by a third officer involved in the search could not have been used to arrest Privette because he wasn't constantly communicating what he knew with the other officers or the district radio dispatcher.

The ruling was not unanimous.

Justice Elspeth Cypher, while agreeing that Privette was properly stopped and that the gun and money could be used against him, said the standard set by the majority for arrests during manhunts would force judges to "consider the inner workings of the minds of each individual officer at the relevant time," a complex task she said was not really needed as long as "the collective knowledge of all officers working together at the time of a stop, search, or arrest," was considered.

"Although I think that communication between officers is a good indicator that they are acting as a team, to inquire into the sufficiency of the communications between collaborating officers in order to aggregate their knowledge will prove difficult for judges trying to apply the new rule, and for officers striving to integrate the court's holding into their daily practices."

Justice Dalila Wendlandt wrote a concurring opinion to the majority one, saying the ruling did not go far enough and that, in some cases,

"[I]t permits an officer to stop (and presumably pat frisk) an individual without beforehand having information constituting reasonable suspicion and without any commonsense reliance on a fellow officer's directions; shockingly, it invites a judge to be complicit in the unraveling of this fundamental constitutional right."