The state’s highest court strengthened the right to privacy Wednesday, ruling that police who want to seize a cellphone cannot rely on a common-sense belief that criminals use cellphones to talk to each other, but instead must have “particularized evidence’’ the phone was connected to a crime.

In a unanimous ruling, the Supreme Judicial Court barred Suffolk District Attorney Daniel F. Conley’s office from using information gleaned from the cellphone of Onyx White, who was charged with the 2010 murder of popular Roxbury store clerk Geraldo Serrano.

During their investigation, Boston police seized White’s cellphone from the Boston public high school he attended. The police did not have a warrant and did not have White’s permission, the court said. Police testified that at least two people were involved in the fatalrobbery, and the investigators’experience showed suspects often used cellphones to communicate with other suspects.

But, writing for the court, Justice Barbara Lenk wrote that the “commonsense notion’’ that suspects use cellphones to communicate with each other — or use it for other tasks, like taking photographs that could be used in evidence — is not enough to override a person’s privacy rights.

“Even where there is probable cause to suspect the defendant of a crime, police may not seize or search his or her cellular telephone to look for evidence unless they have information establishing the existence of particularized evidence likely to be found there,’’ Lenk wrote. “The detectives here lacked any information establishing the existence of evidence likely to be found on the defendant’s cellular telephone.’’

She added, “We conclude, accordingly, that they lacked the nexus required for probable cause to seize that device.’’

White is expected to return to Suffolk Superior Court for a status hearing on the case later this fall. Prosecutors say they are still determined to put White on trial for the slaying.

“It was reasonable to believe that [White and a co-defendant], like countless others, used their cellphones to communicate about the crimes and the identities of the others involved,’’ said Jake Wark, a spokesman for District Attorney Daniel F. Conley. “There was not even a hint of impropriety in the phone’s lawful seizure, careful storage, or court-authorized search. . . . We just don’t see the prejudice.’’

Attempts to reach Boston police and several law enforcement groups to comment on the ruling were unsuccessful on Wednesday.

J.W. Carney Jr., a lawyer for White, praised the ruling and said the prosecution's case against the now-23-year-old White will be “significantly weakened,’’ since the SJC barred the use of any evidence gleaned from the cellphone.

“This is an important decision concerning the right of privacy,’’ Carney said. “We use cellphones to store very personal information. A search of it exposes all aspects of a person’s life.’’

Daniel S. Medwed, a Northeastern University law professor, said the ruling could “potentially have vast ramifications on police conduct’’ in Massachusetts.

“I think the police will now be more deliberative in seeking cellphones [by] making sure they have enough evidence to obtain a warrant before they even seize’’ them, he said.

The SJC said that if it approved the seizure of White’s cellphone on the grounds that it might contain evidence, police and prosecutors would use the argument in every single investigation.

“It would be a rare case where probable cause to charge someone with a crime would not open the person’s cellular telephone to seizure and subsequent search,’’ Lenk wrote. “We cannot accept such a result’’ because it will violate privacy protections under both the federal and state constitutions.

Serrano, the victim in the fatal robbery, was 71 years old and a grandfather to 28 children.

White was 16 years old when he was charged with participating in the murder of Serrano with Martin Freeles, who was then 17 years old. Freeles has since pleaded guilty to manslaughter and is serving a 15-year sentence.

White allegedly was the triggerman and is facing a first-degree murder charge. He has pleaded not guilty, but has been held without bail since 2010.

Once they seized White’s phone, police did not do anything with it for 68 days. Then they sought a search warrant to examine its contents, discovering information that allegedly linked White to similar armed robberies of convenience store clerks.

Conley’s office and police argued it was a reasonable amount of time because detectives were interviewing multiple witnesses, executed five other search warrants, and were also assigned two other homicide investigation during the nearly 10-week period.

The court said that 68 days was too long, however. Police can hold an item seized without a warrant for a short period while seeking authorization, but must release the item if no warrant is obtained promptly, according to the ruling.

“We do not question that the detectives diligently performed their difficult jobs,’’ Lenk wrote, but she also said, “The Commonwealth has not shown that the prolonged delay following the warrantless seizure was reasonable.’’

Wark noted that the SJC held oral arguments on the case on Dec. 8, 2015, and did not issue a ruling until Wednesday, well past the court’s own rules to issue a decision 130 days after hearing from lawyers in the case.

“To what do they attribute the 275-day delay between hearing oral arguments and issuing this decision?’’ Wark said.