Aaron Hernandez -- THE SMOKING GUM

Prosecutors believe they have a CRUCIAL piece of evidence that proves Aaron Hernandez murdered Odin Lloyd ... and the proof tastes like cotton candy.

As Aaron stood shackled in a Massachusetts courtroom moments ago, prosecutors spelled out their case against the former New England Patriots player.

During the hearing, prosecutors say they can prove Hernandez stopped at a gas station hours before the murder and purchased gas, cigarettes and BLUE COTTON CANDY FLAVORED BUBBLICIOUS BUBBLE GUM.

After Odin was murdered, investigators say they found a shell casing in his rental car that matched the caliber of the bullet used to kill the 27-year-old ... and next to the casing -- A CHEWED PIECE OF BLUE COTTON CANDY FLAVORED BUBBLICIOUS BUBBLE GUM.

Officials believe the gum places Hernandez at the scene of the crime -- and proves he killed Odin.