BOSTON – Privacy advocates told Massachusetts’ highest court Thursday that authorities should be forced to get warrants to obtain certain cellphone records that can be used to track a person’s whereabouts.

The arguments before the Supreme Judicial Court stem from a 2011 cold-case murder arrest of Shabazz Augustine.

Authorities obtained cellphone company records to try to determine Augustine’s whereabouts in the days before and after a woman he dated, Julaine Jules, was killed in August 2004. But that evidence was suppressed earlier this year after a Superior Court judge ruled that obtaining the records amounted to a “warrantless search.”

Suffolk County prosecutors then appealed, and Augustine, 34, remains jailed without bail on a first-degree murder charge. No trial date has been set, pending the SJC ruling.

On Thursday, prosecutor Cailin Campbell argued that Augustine hadn’t proven that any search occurred or that the information obtained was specific enough to amount to an invasion of privacy.

But attorney Matthew Segal of the American Civil Liberties Union said that the records request was intrusive and the government should need a warrant to get such information.

“There was no check on what the Commonwealth would get, could get or did get,” he said.

Without forcing authorities to meet the requirements built into the process of obtaining a warrant, Segal said, “there is essentially no protection for the privacy of the many people who are subject to these requests.”

The cellphone records included Cell Site Location Information, which show which cell towers a user’s phone communicates with at the beginning and end of a call. With that information, it’s possible to tell which cell sites a person’s cellphone was near – and by proxy the person – during the length of a call.

Detectives investigating Jules’ slaying received about two weeks of records from a phone Augustine used around the time Jules was killed. In an affidavit accompanying the records request, a state trooper said the records could help prove or disprove Augustine’s claim that the last time he saw Jules was several days before her death.

On Thursday, Segal argued that cellphone use is so common that Cell Site Location Information can be used to reveal intimate details about people’s lives, simply by tracking where they were when they made various calls. He said the state asked for the records, figured out what was on them, and is now wrongly claiming it really wasn’t a search that needed a warrant.

“We don’t determine whether the search of a bag is unconstitutional by looking at what was found in the bag,” Segal said.

But Campbell argued Augustine is overstating how much private information the cell site records reveal, portraying them in this case as similar to GPS data, when it’s not nearly as exact.

“There’s nothing to indeed prove that they do regularly provide this type of (private) information,” she said.

The precision of the information matters because a defendant has no expectation of privacy, for instance, if the record generally shows he was in one town and not another, she said.

Campbell asked the court to either reverse the ruling or sent the case back to the lower court for an evidentiary hearing that could determine just how much information the cell site records offer. Until then, she said, “We don’t know enough about these records to make the finding the defendant asks this court to make.

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