The Los Angeles Times reported Tuesday that the gun has been traced back to a gang in Portland, Maine.
According to the Times, the weapon was originally purchased legally in 2011 at a Cabela's store in Maine by a man named Danny Sun Jr., a Los Angeles native living in a Portland suburb. Sun was arrested on May 1 last year, on a warrant related to a traffic case. But government sources told the Times that Sun was questioned about the gun, and told police he had given it to a man named Biniam Tsegai, an immigrant from Eritrea with a long rap sheet who goes by the name "Icy."
On May 23, 2013, Tsegai was arrested on a warrant connected to a 2009 robbery, and he was later charged with conspiracy to distribute and possession with intent to distribute crack cocaine, according to the Times.
That's as far as the gun's trail goes.
But according to the Times, authorities believe that Tsarnaev's ties to illegal drug trade in Maine helped pay for his trip to Chechnya and Dagestan in early 2012, where he reportedly radicalized.
Tsarnaev's younger brother, Dzhokhar Tsarnaev, is facing 30 federal charges for his alleged role in the bombing.