Police believe Hernandez rented the silver SUV that was linked to the scene of the double homicide in Boston's South End. Police searched for the vehicle for nearly a year before locating it.
Now, state police sources say a gun recovered in a June traffic accident positively matched the weapon used in the double killing.
After the June 21 four-car crash on in Springfield, Massachusetts, Jailene Diaz-Ramos, 19, was taken to a hospital.
Massachusetts State Police conducted a search of her vehicle -- customary for cars towed from accident scenes -- and found the firearm along with several rounds of ammunition.
The gun's ballistics matched bullets recovered in the Boston double homicide last year. According to a police source, the teenager told officers the .38-caliber Smith and Wesson revolver belonged to her boyfriend and that "he was the last one to use the car to visit a football player."
Police say Diaz-Ramos and her boyfriend are both from Bristol, Connecticut, Hernandez's hometown, though their connection is unclear at this time.
Hernandez is separately being held without the bail on first-degree murder charges in the death of his friend and semi-pro football player Odin Lloyd, to which Hernandez pleaded not guilty.
The newly discovered evidence has been presented to a grand jury hearing details of the double homicide case.