(CNN) -- A witness sources have described as Aaron Hernandez's "muscle man" says he was with the ex-New England Patriot the night of a 2012 Boston double homicide that police say may be linked to Hernandez, said a law enforcement source with knowledge of the investigation.
The witness, Alexander Bradley, has filed a civil lawsuit accusing Hernandez of shooting him in the face during an argument after they left a Florida strip club in February. Bradley lost sight in one eye because of the incident, according to the lawsuit.
In what could be a crucial account for the prosecution, Bradley is telling investigators that he was at Boston's Cure nightclub -- with Hernandez -- on July 12, 2012, before Daniel Abreu, 29, and Safiro Furtado, 28, were fatally shot in their car, the law enforcement source said. Bradley and Hernandez were also captured on the nightclub's security camera, the source said.
Bradley has testified before a grand jury in Boston after being arrested last week because he failed to show up for a court proceeding about a grand jury subpoena.
A Boston grand jury has been hearing evidence allegedly linking Hernandez to the double homicide, sources have told CNN.
Among the evidence is a .35 caliber handgun sources describe as the murder weapon in the double homicide.
In addition, a silver SUV driven by Hernandez was discovered covered with dust in his uncle's garage, law enforcement sources say. Law enforcement sources say the SUV is believed to be linked to the deaths.
Hernandez's lawyers have not commented about the investigation.
The SUV was found as investigators searched the uncle's home in Bristol, Connecticut, in connection with another shooting death, that of Odin Lloyd. Hernandez is charged with Lloyd's murder and has pleaded not guilty. He appeared in court Wednesday for a pretrial hearing in that case.
Prosecutors say Hernandez orchestrated Lloyd's June 17 execution-style shooting.
Authorities have said that Hernandez, Wallace, and a third man, Carlos Ortiz, picked Lloyd up from his Boston apartment in a rental car shortly before his death.
Surveillance cameras then captured the rental car leaving the crime scene and Hernandez carrying a gun as he returned to his home minutes later. He was with two other people. Lloyd was not among them.