Late one Saturday evening, Joe and Mark decide to rob a local convenience store.

Mark has a loaded shotgun for the robbery, but both men agree beforehand that the shotgun is only to “scare” the cashier into giving up the money. During the robbery, however, the cashier unexpectedly pulls out a handgun and points it at the two men. Mark panics, pulls the trigger on the shotgun, and kills the cashier. Joe is being charged as an accomplice to both robbery and murder. Is Joe an accomplice to murder? Why or why not?