( CNN ) -- Former New England Patriots tight end Aaron Hernandez is being investigated by a Massachusetts grand jury for possible gun trafficking , a source with knowledge of the investigation told CNN on Monday . The news comes one day after Massachusetts State Police served one of Hernandez 's former college teammates , Mike Pouncey , with a subpoena related to the investigation , sources confirmed to CNN . After the Patriots defeated the visiting Miami Dolphins 27-17 at Gillette Stadium , police officers in suits gave Pouncey , a center for the Dolphins , a piece of paper in a hallway between a locker room and the Dolphins ' bus , Sports Illustrated first reported . The gun trafficking investigation deals with illegally transporting weapons across state lines and , in part , involves the discovery of an assault-style rifle hidden in a vehicle rented in Florida and later found in Massachusetts , according to a separate law enforcement source . CNN requested comment from the Dolphins , the NFL , the Massachusetts State Police and the district attorney 's office prosecuting the Hernandez cases in Bristol County , Massachusetts . Representatives from each declined to comment . Hernandez , 23 , was charged in August with first-degree murder in the June shooting death of his friend Odin Lloyd . The grand jury investigating the allegations of gun trafficking is the same one that handed up the murder charge , a source said . Pouncey , 24 , has not been charged in any possible wrongdoing and was asked to appear as a witness . He and his twin brother , Maurkice , both attended the University of Florida with Hernandez . After Hernandez was arrested in June after the execution-style killing of Lloyd , a photo of the Pouncey brothers at a night club wearing baseball caps that read `` Free Hernandez '' was posted on Twitter July 14 . Maurkice Pouncey , a center for the Pittsburgh Steelers , later posted a statement , apologizing and saying it `` made light of a serious situation . '' According to Sports Illustrated , a Steelers spokesman declined to comment when asked whether Maurkice Pouncey had been served . The Steelers will play at Gillette Stadium on Sunday . Hernandez was arrested in late June , 10 days after authorities say Lloyd , a 27-year-old semi-pro football player , was killed in North Attleborough , Massachusetts . Authorities have said that Hernandez , Ernest Wallace and Carlos Ortiz picked Lloyd up from his Boston apartment in a rental car shortly before he was found shot to death on June 17 in an industrial park not far from Hernandez 's home . Hernandez pleaded not guilty in September to a charge of first-degree murder . Wallace and Ortiz have pleaded not guilty to charges of being an accessory to murder after the fact . Hernandez is also under investigation by a different grand jury in Boston looking into the unsolved 2012 double homicide of Daniel Abreu and Safiro Furtado outside a Boston nightclub .
Source : Grand jury that handed up murder charges considers gun trafficking allegations . Sources : Former college teammate Mike Pouncey served subpoena after game Sunday . Second case concerns weapons transported across state lines , second source says . Aaron Hernandez also is charged with murder in the June death of Odin Lloyd .