(CNN) -- Almost a year and half after the Boston Marathon bombing, we have a partial answer to one of the key questions surrounding the investigation:
Where the did the gun come from allegedly used by the Tsarnaev brothers to kill MIT officer Sean Collier four days after the bombing?
Stephen Silva, a 21-year-old Cambridge resident, is the source, according to a law enforcement official who requested anonymity because full details have not been released.
A grand jury indictment was unsealed Tuesday charging Silva with a single firearms possession count and seven additional heroin charges.
Court documents state that in February 2013, two months before the April 15 bombing that killed three people and injured more than 260 others, Silva possessed a Ruger P95 semiautomatic handgun that had the importer and manufacturer's serial number "removed, obliterated and altered," according to the indictment.
That same model has been previously identified as the murder weapon.
In court papers, there is no mention of the Boston bombing or Dzhokhar and Tamerlan Tsarnaev. However, the law enforcement official tells CNN Silva has been identified as the person who allegedly provided that same gun used to kill Collier.
Silva made an initial court appearance Tuesday.
His court-appointed attorney, Jonathan Shapiro, told CNN that despite reports it is the same weapon allegedly used by the Tsarnaev brothers, that has not been charged, let alone mentioned, in the indictment.
"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. Out of respect for that system and for my client I cannot make any further comment on the case," Shapiro said Tuesday evening.
Shapiro would not comment on whether his client has a previous relationship with either of the Tsarnaev brothers.
The U.S. Attorney¹s Office and FBI offered no comment. CNN has not been able to contact the Cambridge Police Chief for whom Collier worked.
Silva's next scheduled court appearance is August 6.
CNN's Rande Iaboni contributed to this report