The murder trial for alleged Tupac Shakur killer Duane "Keefe D" Davis rolls into Day 2 ... and it's expected to be wild after yesterday's opening arguments, which were 30 years in the making.

As TMZ reported ... Keefe is accused of planning the murder of the legendary rapper and allegedly produced the gun used to kill Tupac ... though prosecutors say he wasn't the trigger man that fateful night.

He has pleaded not guilty to all charges against him.

The trial's taking place in a Nevada courtroom ... nearly 3 decades after Tupac was gunned down near the Las Vegas Strip while riding as a passenger in Suge Knight's BMW.

One of the most interesting moments so far ... a cop who rode with Pac to the hospital after he'd been shot testified that the rapper refused to say who shot him.

The former cop said Tupac made it clear his posse would take care of the gunman.

If convicted, Keefe faces life in prison.