Newly released video footage of the arrest of Sandra Bland, who died in a Texas jail of unknown causes, shows the exact point when the black 28-year-old woman's death could potentially have been prevented. It happens when Texas trooper Brian Encinia utters seven simple words: "You mind putting out your cigarette, please?"

Bland doesn't cooperate. She responds, "I'm in my car. Why do I have to put out my cigarette?" Encinia then demands Bland get out of the car. She refuses. He tries to yank her out. She won't budge. He pulls out his Taser and yells, "I will light you up." The situation escalates.

But what if Encinia hadn't uttered those seven words in the first place, or let Bland keep smoking her cigarette even after he asked her not to?

It's hard to see what harm would have come out of the traffic stop. Bland would keep smoking her cigarette. Encinia would give her a warning or ticket for failing to signal when she changed lanes. Bland would leave, and Encinia would continue his patrol. No harm would have come to Encinia or the public if Bland had just been allowed that one refusal. In fact, it might have reduced harm — a struggle wouldn't have taken place, Bland wouldn't have been arrested, and she wouldn't have died in that jail cell (authorities are still determining whether her death was a suicide or homicide).

It's true that Bland could have just obeyed, and the situation may not have escalated. But smoking isn't illegal, so Bland wasn't violating any laws by smoking in her car. (Although, as Reason's Jacob Sullum pointed out, that may not give Bland the legal right to disobey the cop.)

"Your mission is not to provoke. It is to deescalate. It is to ease tension."

But it's the police officer's — not the civilian's — explicit job to make sure a situation doesn't escalate. Failure to do this was the main complaint of how law enforcement handled the Ferguson, Missouri, protests after the police shooting of Michael Brown last August: They consistently used too much force, even against relatively peaceful crowds, causing the situation to spiral into mayhem.

Back then, Norman Stamper, former Seattle police chief, told Vox's Amanda Taub, "First order of business is to make sure that you know, as a law enforcement agency, what your purpose is, and that is to deescalate. In other words, your mission is not to provoke. It is to deescalate. It is to ease tension. And if everyone knows that that's the mission, that's a huge step forward — a huge advancement, frankly, over where we are in many law enforcement agencies."

This is where the criminal justice system first failed Bland. By asking Bland to put out her cigarette, and getting visibly upset when it didn't happen, Encinia allowed the situation to escalate, and was then forced to arrest her. And that eventually landed Bland in jail, where she died three days later.

Watch: Why it's so important to film the police