Last Updated Jul 22, 2014 10:45 PM EDT
BOSTON - A friend of Boston Marathon bombing suspect Dzhokhar Tsarnaev is believed to have provided the handgun used to kill a Massachusetts Institute of Technology police officer during the manhunt, a law enforcement source told CBS News.
Stephen Silva made an initial appearance in federal court Tuesday on charges related to heroin trafficking and possession of a handgun with an obliterated serial number.
The grand jury indictment against him does not mention any connection to Tsarnaev or the slaying of MIT police officer Sean Collier. But a law enforcement source told CBS News senior producer Pat Milton that investigators allege Silva provided the gun that was used to kill Collier.
An attorney for Silva, Jonathan Shapiro, said Tuesday evening that he had received the case only a few hours earlier.
"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 April 2013 attack, in which three people were killed and more than 260 were injured when twin bombs exploded near the marathon finish line. Collier, a 26-year-old MIT campus police officer, was ambushed a few days later and shot multiple times in his car.
According to the indictment, Silva knowingly had possession of a 9 mm Ruger pistol, "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.
A neighbor told CBS Boston he witnessed Silva's arrest in Cambridge Monday night.
"They rolled up packed," the man said. "There was like 15, 16 cars everywhere in the courtyard. I was in a meeting, I was on my way home and then someone screamed, 'The feds are downstairs!' I ran, I looked I saw them carrying big cases."
Silva is a friend of Dzhokhar Tsarnaev. He said in court Tuesday that he graduated from Cambridge Rindge and Latin School in 2011, the same year as Tsarnaev. 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 several days after the bombings. Dzhokhar Tsarnaev escaped but was soon found, 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. Tazhayakov and Kadyrbayev are both natives of Kazakhstan.
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.