The Supreme Judicial Court on Friday set out ways that police can subpoena tens of thousands of cell-phone records to try to link specific phone calls to crimes, in a case in which they used the technique to connect a Canton man to the murder of Jose Luis Phinn Williams at a Washington Street gas station and to a series of other similar, if less deadly, robberies that year in Mattapan, Canton and Cambridge.

In a ruling involving the way Boston Police obtained and then sifted through more than 50,000 cell-phone records from seven different cell towers to find proof that Jarron Perry and Gregory Simmons teamed up to rob and then murder their victim, the court said police had shown enough probable cause to justify a warrant for the search - that they had shown the two were suspects and provided sufficient evidence to a judge that the nature of the crimes and the proof they had collected to that point would likely be buttressed by finding their phone-numbers attached to calls made through the towers.

But the court also acknowledged that the large potential for abuse with a collection of thousands of potentially privacy-infringing data points, so it also ruled that going forward, police need a search warrant for all "tower dumps" from a superior-court judge and that the application needs to include "protocols for the prompt and permanent disposal of any and all data that does not fit within the object of the search following the conclusion of the prosecution."

This means the information can be used as evidence In Perry's trial for the murder of Phinn Williams on Oct. 6, 2018, just a few days before his 68th birthday, as he worked at the Fabian gas station in Dorchester's Codman Square.

Police initially arrested one man for his murder, but they realized they had the wrong man and the DA's office dropped charges.

Simmons, who was not a party to the suit that led to today's SJC ruling, was arrested several months later for the murder, a month after Perry was arrested on charges of robbing a Mattapan phone store and other businesses across the area. He was also indicted as the shooter in Phinn Williams death, although, unusually, the DA's office never announced that - the SJC case was the first time his name publicly surfaced in regard to the murder.

In its ruling, the SJC first laid out the groundwork of overlaying privacy rights that date back hundreds of years to technology that, if allowed unfettered, would allow police to surveil in great detail the daily lives of everybody who uses cell phones, specifically in this case to "tower dumps" of "cell-phone location information" collected from just before to just after the various robberies and the one murder from seven specific cell towers near the crime scenes.

"There is no historic analogue for the ability effortlessly to compile and document the locations, identities, and associations of tens of thousands of individuals, just in case one might be implicated in a criminal act. Even if such a feat were possible, it certainly would be impossible to execute surreptitiously; yet, here, investigators were able to compile and catalogue the locations of more than 50,000 individuals at varying points over more than one month, without any one of them ever knowing that he or she was the target of police surveillance."

It noted the particularly thorny issue of obtaining records that span a period of time - which can show patterns in a person's life that could make that life an open book to investigators, laying bare details of his daily life and associations that are supposed to be protected by both the Fourth Amendment and the similar, if even more privacy supporting, section of the state constitution.

To comport with constitutional protections, an affidavit in support of a search warrant for CSLI must demonstrate "probable cause to believe [1] 'that a particularly described offense has been, is being, or is about to be committed, and [2] that [the CSLI being sought] will produce evidence of such offense or will aid in the apprehension of a person who the applicant has probable cause to believe has committed, is committing, or is about to commit such offense'" (alterations in original). Estabrook, 472 Mass. at 870, quoting Augustine I, 467 Mass. at 256.

It then turned to the specifics of two search warrants for the data, one requested by an FBI agent, one by a BPD detective. State courts normally do not rule on warrants obtained by FBI agents in federal court, but the court said it had jurisdiction in this case because the primary reason for the search involved a state crime - Phinn Williams's murder.

The court concluded that the warrant obtained by BPD, which resulted in data that showed Perry's phone number near crime scenes - police had his number from when he once filed a report on a car accident - as well as Simmons's - justified a search warrant because police were able to show sufficient evidence they already had reason to suspect the two, rather than simply going on a fishing expedition.

"Here, it is undisputed that the Commonwealth established probable cause to believe that the offenses described in the warrant had been committed. Accordingly, we consider whether each warrant affidavit established a substantial basis to believe that a search of the requested tower dumps would produce evidence of the crimes under investigation, or would aid in the apprehension of the perpetrator.

"The second search warrant affidavit [the one applied for by Boston Police] described several notable similarities between the offenses. Each robbery, as well as the attempted robbery, was committed against a clerk at a store, almost always a convenience store, in or around Boston, sometime during the period between dusk and dark. The perpetrator always brandished a black semiautomatic pistol, which he held in his right hand. Witnesses consistently described the perpetrator as a light-skinned Black or Hispanic male, approximately six feet, two inches tall, with a medium to thin build, dressed in a black hooded jacket, dark-colored pants, black gloves, black shoes, and a black or red mask. In addition, on two occasions, surveillance footage showed a hole or a light-colored blemish on the robber's jacket. Collectively, this evidence provided a substantial basis to believe ... that the same individual had committed all of the offenses. ..

"The second warrant affidavit also described evidence indicating that a suspected coventurer had acted as a getaway driver in at least three of the offenses under investigation. The robberies took place from two to eleven miles apart, and some of the locations were not near any public transportation. On October 4, 2018, the store clerk saw the perpetrator enter the passenger's side of a dark-colored sedan, without removing his mask, before quickly departing the scene. On October 6, 2018, a surveillance camera recorded video footage of a dark- colored sedan or coupe traveling at a high rate of speed along the perpetrator's path of flight, as recorded by a separate surveillance camera. Moreover, on October 31, 2018, police canines detected the perpetrator's scent along his reported flight path, but the scent ended abruptly in a public area with no nearby public transportation, which could have indicated that the perpetrator entered a vehicle.

"The search warrant affidavit also described facts suggesting some reason to believe that the defendant and a coventurer had communicated with one another from a distance, either prior to or after the commission of the offense. The detective seeking the search warrant averred that, based on his experience and training, violent crimes such as those at issue often require some level of coordination amongst coventurers.

"Because there was reason to believe that the perpetrator used a cellular telephone to communicate with a coventurer around the time of the offenses, there also was probable cause to believe that either the perpetrator's telephone or the coventurer's telephone would have produced telephone call CSLI that would appear in the requested tower dumps, and likely in more than one of the tower dumps. This CSLI, in turn, would enable investigators to isolate potential suspects by determining which, if any, individuals had been near the scene of two or more of the offenses."

The court acknowledged that the first search warrant, the one the FBI sought in federal court, had similar information about the crimes. However, the court continued, it provided no evidence that the alleged criminals had used cell phones in the commission of the crimes and so was invalid, at least in Massachusetts courts.

"[T]he first warrant affidavit did not discuss the need for coventurers to communicate when committing a robbery, nor did it point to any evidence that the perpetrator and the coventurer had been separated during the commission of the crime such that they would have had to communicate from a distance.

"Thus, the only ground in the first affidavit upon which to conclude that the perpetrator had possessed or used a cellular telephone to aid in accomplishing the crimes was the affiant officer's statement that 'it is very common for a person to have a cellular telephone with them at all times.'"

And that, the court said, is not good enough to justify the sort of privacy invasion that would come with a police search.

The court rejected an argument by Perry's attorney that even the warrant the court accepted was unconstitutional, because police essentially searched the records of thousands of other people who had nothing to do with the alleged crimes.

"A cursory examination of anonymized CSLI would not permit investigators to infer the identity of any given individual, where within the cell site's radius that person had been, or with whom he or she had associated; thus, such an examination would not intrude upon a reasonable expectation of privacy. The question, then, becomes whether the second warrant sufficiently limited the set of telephone numbers and their associated CSLI that investigating officers were permitted to analyze, and therefore to search."

Specifically, the court said that because the affidavit filed by a detective for the warrant sought permission only to "identify and/or verify commonalities" between numbers that appeared in two or more of the "tower dumps," not all of them, so it was narrow enough in scope to not intrude on the privacy of thousands of people:

"Otherwise put, because the warrant authorized the search of only a narrow subset of the CSLI, for purposes of identifying a common suspect, it was sufficiently particular."

Filings in the case, including arguments by prosecutors and Perry's attorneys and amicus briefs by privacy and civil-rights groups.