We do not know enough about the interaction between Dr. Dao and the Chicago Aviation Department security officers to tell if the escalation to violence was reas

We do not know enough about the interaction between Dr. Dao and the Chicago Aviation Department security officers to tell if the escalation to violence was reasonably graduated or not. There are accepted general practices for such escalation, and a common one is the command voice, for example. There is no way now to discover if policy and common practice was applied by the officers on the scene, unfortunately.