Many armchair commenters are arguing over when the "inciting incident" occurred. Who—Sandra Bland or the cop—took the action that propelled their interaction to its horrible conclusion? It could have been the moment Bland decided to drive while black in Texas. It could have been the moment she decided to light the cigarette, a small salve against the indignity of being made to wait seemingly forever while a ticket is being written. It could have been the moment she didn't form her countenance to flatter his authority. It could have been the moment when the cop asked her to step out, or the moment he opened her door, or the moment he pulled out his taser and said "I'm going to light you up."
That's the moment, in my opinion, when he admits that he hasn't been policing his imagination, that he's been letting it run wild with racist assumptions and specious arguments about black people and crime.