A 21-year-old Massachusetts man is believed to have provided the gun used by the Boston marathon bombing suspects to kill an MIT police officer while on the run from authorities, according to reports.

Stephen Silva, of Cambridge, Mass., made an initial appearance in federal court Tuesday on charges of related to heroin trafficking and possession of a handgun with an obliterated serial number. WFXT, citing two sources, reported that authorities have linked the gun to the murder of Sean Collier, who was shot last April 18 while sitting in his police cruiser.

The gun described in the grand jury indictment is a 9mm Ruger pistol, the same type of gun used to kill Collier. The indictment, which was filed July 15, does not mention Collier's slaying or any connection to the Tsarnaevs. A spokeswoman for the U.S. Attorney's Office said she could not confirm that the gun was connected to Collier's killing.

A neighbor of Silva told WFXT that Silva was arrested Monday evening at his Cambridge apartment. The neighbor added that the apartment was searched by approximately 20 federal agents, who removed boxes from the apartment.

Another neighbor said that Silva was good friends with bombing suspect Dzhokhar Tsarnaev, since the pair attended high school together. Silva said in court Tuesday that he had graduated from high school in 2011, the same year as Tsarnaev.

An attorney for Silva, Jonathan Shapiro, told The Associated Press Tuesday evening that he had received the case only a few hours earlier.

"According to news reports, law-enforcement officials say it is the same weapon that was used ... in the MIT officer Sean Collier shooting. However, this has not been charged in the indictment," Shapiro said.

"I am in the process of meeting with my client and reviewing the available evidence which will eventually be presented in a court of law in accordance with our system of justice," Shapiro said in a statement. "Out of respect for that system and for my client, I cannot make any further comment on the case."

The origin of the gun was among the lingering mysteries of the investigation into the marathon attack, in which three people were killed and more than 260 were injured when twin bombs exploded near the finish line.

According to the indictment, Silva knowingly had possession of the gun, "which had the importer's and manufacturer's serial number removed, obliterated, and altered and had previously been shipped and transported in interstate and foreign commerce."

The indictment also alleges that Silva conspired to distribute heroin this summer in the Boston area.

Silva was ordered to remain in custody ahead of a bail hearing scheduled for Aug. 6.

Dzhokhar's brother, Tamerlan Tsarnaev, was killed in a shootout with police early on the morning of April 19, four days after the bombings. Dzhokhar Tsarnaev escaped but was found later than day, wounded and hiding in a boat dry-docked in a backyard in suburban Watertown.

Dzhokhar Tsarnaev has pleaded not guilty and is scheduled for trial in November. He faces the possibility of the death penalty if convicted.

Four other men have been charged with crimes related to the bombing investigation.

On Monday, a federal jury found Azamat Tazhayakov guilty of obstruction of justice and conspiracy for trying to protect Tsarnaev by agreeing with another friend, Dias Kadyrbayev, to get rid of a backpack and disable fireworks they took from his dorm room. Kadyrbayev is to be tried next month on the same charges.

Robel Phillipos, who is charged with lying to investigators about being in the dorm room with Kadyrbayev and Tazhayakov the night the items were taken, is to have a separate trial in September. And a friend of Tamerlan Tsarnaev, Khairulluzon Matanov, is to be tried next year on charges that he lied to investigators about the extent of his friendship with Tamerlan Tsarnaev and the contact he had with both brothers in the days following the bombings.

The Associated Press contributed to this report.

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