It could be the closest thing to a smoking gun ... prosecutors just played video in court showing Aaron Hernandez holding a firearm in the hours after he allegedly killed Odin Lloyd.
Prosecutors say the footage was taken inside Hernandez's Massachusetts house on June 17, 2013 ... showing the forming NFL star clutching what appears to be a glock firearm.
Officials believe Lloyd was shot 6 times earlier that morning ... and are convinced Aaron pulled the trigger using the very same gun in the surveillance video.
Opening statements in the murder case just wrapped up. Stay tuned ...