Last week, A Las Vegas Grand Jury indicted Keefe on one count of murder using a deadly weapon, plus a gang enhancement in the 1996 death of Tupac Shakur.

2Pac was murdered after a Mike Tyson fight in Las Vegas.  He was riding in a car with Suge Knight when he was killed in a driveby.

Keefe and three other men -- including the alleged shooter Orlando Anderson -- were in the other car.

Suge and Keef are the only two still alive.

However, Suge tells TMZ he will not under any circumstances testify against Keefe, whom he's known since they were kids.

Suge also said that he doesn't believe Anderson was the shooter.  But he won't say who was.

Suge is currently serving a 28-year sentence for voluntary manslaughter in an unrelated case.