Sounds like they got a call off stating they were doing a precautionary landing secondary to transmission caution or warning light, and that was the last transmission.
Have seen some pics where the rotor system both main and tail were relatively intact. If I had to guess I would say the transmission seized up completely, which if that happens you cannot uncouple the transmission and enter an autorotation, and thus would just fall to the ground. Definitely looks mechanical though, and really want to follow up on the cause. These A/C are built to fly for 10-15 minutes without oil as a safe guard so really curious as to what happened.
Regardless it's a huge loss of life, makes me ponder what I do for a living now that I am married and no longer just worried about myself, and my thoughts and prayers are with the entire Duke team.