Metro

Tsarnaev friend linked to gun tied to Collier murder to change plea

A Cambridge Rindge and Latin alumnus charged with possessing a gun that was allegedly used later by the Boston Marathon bombing suspects to kill an MIT police officer is set to plead guilty on Friday, according to court records filed Monday.

The development suggests that Stephen Silva, 21, who had previously pleaded not guilty to a series of drug and weapon charges, has agreed to plead guilty to at least some of the charges in return for government leniency, and, given the timing, raises the strong possibility that he will testify against Dzhokhar Tsarnaev, his former high school classmate who is charged in the bombings and the officer’s slaying.

Court records did not give any specifics of the change of plea, and Silva’s lawyer, Jonathan Shapiro, did not return phone calls to his office Monday.

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Mark Pearlstein, a former veteran federal prosecutor in Boston, said the timing of the plea deal is curious, coming about four months after Silva’s arraignment and only two weeks before the start of Tsarnaev’s trial. Pearlstein said he has no first-hand knowledge of the plea, but he would expect prosecutors in the Tsarnaev case to seek Silva as a witness and make a plea deal before the trial begins.

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Aside from the federal gun charge, Silva has been accused of conspiracy to sell heroin and possession of heroin on six occasions in June in Medford. The conspiracy charge is the most serious offense he faces; if convicted, he would face a prison term of five to 40 years.

Pearlstein, who is now a lawyer with McDermott Will & Emery, said that if a plea arrangement made Friday is sealed, that would further suggest Silva is providing critical testimony in the upcoming high-profile bombing case.

In exchange, prosecutors could recommend a lighter sentence.

Meanwhile, a relative of Silva’s, who asked not to be named to avoid involvement in the case, said he has spoken with Silva on the phone since his arraignment, most recently around Thanksgiving, but had not yet heard about a plea deal.

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Silva graduated from Cambridge Rindge and Latin with Tsarnaev. The two also worked together as lifeguards at Harvard University’s main pool and were close friends.

Tsarnaev and his older brother, Tamerlan, are accused of setting off two bombs that killed three and injured 260 others on April 15, 2013. A few days later, after the FBI published photos of the alleged bombers, the brothers went on the run and allegedly killed Massachusetts Institute of Technology police officer Sean Collier in a failed effort to get his gun, officials said.

Tamerlan later died in a shootout with police in Watertown. His brother was captured in a dry-docked boat behind a Watertown home.

During the shootout with police, agents found a weapon — a Ruger P95 9mm — that they say was used in the killing of Collier. Federal prosecutors have charged Silva with possessing a gun of that exact model in February of 2013, two months before the bombing.

While prosecutors have not explicitly said that Silva provided the gun to the Tsarnaevs, Silva’s attorney said he was told by federal authorities that the gun charge is related to the MIT officer’s death.

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Dzhokhar Tsarnaev has pleaded not guilty to numerous charges, including some that carry the death penalty, and is being held without bail. Jury selection is set to begin in his trial in early January.

Patricia Wen can be reached at wen@globe.com. John R. Ellement can be reached at ellement@globe.com. Follow him on Twitter @JREbosglobe.