I coud be completely wrong, but I'd suggest the PIC on UA3411 would bear responsibility for this debacle because of
Vicarious liability which states:
Vicarious liability is a form of a strict, secondary liability that arises under the common law doctrine of agency, respondeat superior, the responsibility of the superior for the acts of their subordinate or, in a broader sense, the responsibility of any third party that had the "right, ability or duty to control" the activities of a violator.
The PIC is responsible for the actions of his Crew and Dispatchers irrespective of whether he knew what was going on or not. I would suspect that the assault on Dr Dao (should he chose to make a formal complaint to the police) could result in criminal charges against the thugs that manhandled him off the flight. This could then extend to the crew who instigated the removal of Dr Dao on the basis there wasn't a valid and lawful reason for his disembarkation. In US law a getaway car driver (an accomplice) is just as guilty of murder as a bank robber who kills someone during a robbery, so using this analogy, the crew could be deemed as accomplices to the assault.