Suffolk County prosecutors have ended their prosecution of three men who were arrested last year after they were seen exiting the Roxbury apartment building of a former English High School dean who had been accused of shooting a 17-year-old student over drugs.

The alleged shooter, Shaun O. Harrison Sr., 56, was indicted last April with Dante Lara, Wilson Peguero Jr., and Oscar Pena, but the case against the latter three men came apart in December when a judge allowed their requests to dismiss all evidence seized during their arrests, court records show.

The decision, filed in Suffolk Superior Court and dated Dec. 21, found a Boston police detective illegally stopped and frisked Lara, Peguero, and Pena at a bus stop near Harrison’s residence on March 4, 2015, a day after the English High student was shot in the head. The teenager survived.

On Jan. 12, Suffolk Assistant District Attorney David S. Bradley notified the court that the state was terminating the prosecution of Lara, Peguero, and Pena.

Lara, 25, and Pena, 20, had faced firearms charges. Pena had also been charged with possession with intent to distribute marijuana, along with Peguero, 24.

Harrison, who rose to prominence in Boston as an antigang activist, is scheduled to face trial May 2 for allegedly shooting the teenager, court records show.

Bradley has said Harrison, the former dean of students at English High, shot the student after he recruited the 17-year-old to sell marijuana for him and then became disillusioned with the teen’s sales. Harrison also has ties to the Latin Kings gang, according to prosecutors. He has pleaded not guilty. His lawyers did not respond to requests for comment.

Lara’s lawyer said prosecutors gave the impression that there was a link between Harrison’s alleged crime and the three men.

“In my opinion, there was no connection between these three guys and what Harrison is charged with, yet they made it seem that way,’’ attorney Arnold I. Abelow said Tuesday.

Boston Police Detective Richard Medina spotted Lara, Peguero, and Pena while he was conducting surveillance of Harrison’s apartment building on Pompeii Street on March 4, 2015, Superior Court Judge Kenneth W. Salinger wrote in his ruling.

He saw the men exit the building and then walk toward Massachusetts Avenue, where Medina found them at a bus stop. Medina, who was dressed in plain clothes, told the men about the shooting and said he saw them leave Harrison’s apartment building. He announced he planned to frisk them, the decision said.

Bradley had argued that Medina stopped the men because he believed they were removing items from Harrison’s apartment.

During the encounter, Medina seized a high-capacity, 9-millimeter, semiautomatic firearm from Lara, police records show. He then threw Lara to the sidewalk and ordered Peguero and Pena to the ground at gunpoint, Salinger wrote.

Medina also found a .45-caliber semiautomatic firearm in Pena’s backpack and some marijuana in Peguero’s backpack, the decision said.

Judge Salinger ruled Medina’s actions were illegal.

“Medina had no reason to suspect that Lara, Pena, or Peguero had committed or was committing any kind of crime,’’ he wrote. “Although Medina testified that he worried that the defendants may be disposing of incriminating evidence on behalf of Harrison, that fear did not even rise to the level of a hunch. It was a wild guess, unsupported by any facts known to the Boston police.’’

Jake Wark, spokesman for the Suffolk district attorney’s office, said the prosecution of the three men could not continue without the evidence Salinger tossed.

“We’re confident, however, that the seizure of two illegal handguns during those arrests likely prevented additional crimes of violence on Boston’s streets,’’ he said.

A Boston police spokeswoman declined to comment, citing the ongoing case against Harrison.

Peguero’s lawyer, James Greenberg, said his client does not plan to testify against Harrison. At Peguero’s apartment Tuesday, a man who answered the door said Harrison is innocent.

Reached by phone, Pena declined to comment. His lawyer did not respond to requests for comment.

Lara is serving a jail sentence for attacking a man with a knife in July 2014. He is scheduled to be released in April, Abelow said.

Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi.