William Mitchell, 5, of Houston, holds a sign at a rally at the Waller County, Tex., Jail protesting the death of Sandra Bland, who died in custody. (Jay Janner/Associated Press)

SANDRA BLAND should not be dead.

The official account of how the 28-year-old African American woman perished in a Waller County, Tex., jail cell this month states that she committed suicide by “self-inflicted asphyxiation.” Her family disputes that Ms. Bland could possibly have taken her own life. Though an official murder investigation is in process, and the Texas Rangers are looking into the case with FBI supervision, there is at present no evidence to disprove the suicide narrative.

But it’s plain to us that Ms. Bland shouldn’t have died in jail — because she never should have been in that cell to begin with. A dashcam video the Texas Department of Public Safety released Tuesday shows that the encounter that led to her arrest and charging spiraled out of control, in large part because of the arresting officer’s confrontational behavior.

Officer Brian Encinia pulled Ms. Bland over for failing to signal before executing a lane change. Over the course of an increasingly testy exchange, Ms. Bland explained that she was irritated because she had been trying to get out of the officer’s way when she switched lanes. Instead of handing Ms. Bland a warning or a ticket and moving on, Mr. Encinia asked her to extinguish her cigarette. Ms. Bland refused. Instead of letting that insult roll off his back, Mr. Encinia ordered her to exit her car. The command unnecessarily inflamed the situation but was legal. What happened next may not have been. Though Ms. Bland committed a minor traffic violation and did not seem to be a threat to public safety, Mr. Encinia forcibly removed her from her car.

Where de-escalation was required, Mr. Encinia escalated. “Regardless of the situation, the DPS state trooper has an obligation to exhibit professionalism and be courteous,” Steve McCraw, the director of the Department of Public Safety, said. “That did not happen in this situation.” No matter what happens with the murder investigation, it won’t change the fact that the encounter should never have gotten so heated, and it was the officer’s responsibility to prevent that.

If it were not already obvious, police officers must assume that they are being recorded at all times. That awareness should underline that they have no option but to be calm and careful, no matter how insulted they feel. We don’t expect that to be easy at all times and in all situations. Yet the police are entrusted with the awesome power to legitimately use force on the public . That trust requires restraint and judgment — among other things about when confrontation is necessary and when it isn’t. We see no reason why Ms. Bland shouldn’t have collected her traffic warning and driven on — annoyed, but alive.