AUSTIN, Tex. — [For more about police violence and unrest, go here]

Sandra Bland had just driven in from Illinois to start a new job in Texas when a state trooper pulled her over for failing to signal a lane change. As the exchange grew angry and the officer pulled out a stun gun, she recorded a 39-second cellphone video whose public broadcast this week has prompted calls for a renewed investigation into her arrest and death nearly four years ago.

Ms. Bland, a 28-year-old African-American from the Chicago area, was taken into custody in southeast Texas following the confrontational 2015 traffic stop and was found hanging in a jail cell three days later in what was officially ruled a suicide. The case, which drew international attention, intensified outrage over the treatment of black people by white police officers and was considered a turning point in the Black Lives Matter movement.

[The Death of Sandra Bland: Is There Anything Left to Investigate?]

The video surfaced for the first time publicly Monday night in an investigative report on the Dallas television station WFAA that included interviews with Ms. Bland’s family and supporters, who accused officials of concealing information that they said should have been made public early in the investigation.