No sounds of movement in the differential? Sounds to me like you need to see the exploded view diagram and look for a broken axle, or something else between the differential and the wheel (can't remember the power path from the diff to the wheel).
Can you put on blocks? If one side is broken it should not turn with any torque (meaning it might turn in gear with the diff lock, simply from drag, but shouldn't have any torque). Come to think of it, it might be obvious if the engine were off and the unit is in gear, diff locked (tires off the ground). One wheel will likely turn, and the other will be locked. The one that turns has "issues".