Aaron Hernandez involved in fight with another inmate in jail

Aaron Hernandez has been indicted on charges he MURDERED two people in a 2012 drive-by shooting ... in addition to the murder of Odin Lloyd.

TMZ UPDATE- 8:40 AM PT -- Officials say they HAVE the murder weapon ... a .38 caliber revolver ... which they believe Hernandez used to kill the two men. 

Officials also believe Hernandez didn't know the victims before a "chance encounter" inside Cure nightclub hours before the shooting. 

After an incident inside the club, Hernandez followed them out ... and trailed them inside his SUV. When the victim's car stopped at a red light, Hernandez opened fire. Killing 2 men and injuring a 3rd. Two other people inside the car fled from the scene on foot. 

Officials say the men were "two young innocent victims" who had NO gang connections whatsoever.