Dashboard camera video has been released showing the arrest of a woman in Texas who was found dead in her jail cell three days later.
Sandra Bland, a 28-year-old black woman from the Chicago area, was pulled over on 10 July in Prairie View, Texas, northwest of Houston, for failing to signal a lane change.
The 52-minute video, released by the Texas Department of Public Safety, shows state trooper Brian Encinia approaching the car and asking if Ms Bland is irritated.
She replies that she is upset about being stopped for such a minor issue.
After running a check of Ms Bland's driving history, the trooper returns and asks her to put out her cigarette, which she refuses to do, saying she has the right to smoke in her own vehicle.
At that point, the video shows the state trooper demanding she leave the vehicle and then trying to pull her out.
Warning: Graphic content in video
He then points a Taser and shouts: "I will light you up."
Ms Bland asks at least ten times why she is being arrested and for what offence before the state trooper replies she is resisting arrest.
She is heard telling the trooper: "I can't wait until we go to court."
Ms Bland, who was taken into custody and later charged with assaulting an officer, was found dead in her jail cell three days later.
Her death was originally ruled a suicide.
But her family, while acknowledging that Ms Bland previously posted a video blog saying she was struggling with depression, has dismissed the idea she was suicidal.
Family members said she was excited about starting a new job at her alma mater, Prairie View A&M University.
Waller County District Attorney Elton Mathis said on Monday he would investigate her death as a homicide.
The state trooper has been put on desk duty for violating protocol in the arrest, officials have said.
Demonstrators have protested outside the jail where Ms Bland died and her case has been taken up by activists who say it is the latest example of racial bias and excessive force by US law enforcement.
The trooper involved in the incident is white.
Ms Bland's family has called for an independent autopsy and involvement by the US Department of Justice in the investigation of her death.
A memorial for Ms Bland was held at Prairie View A&M last night.
"I am angry because of the way she died," Ms Bland's mother, Geneva Reed-Veal, said at the memorial.
"All I want to know is why."
A Texan politician, speaking at a news conference yesterday, said the video suggested Ms Bland should never have been arrested in the first place.
Democratic state Senator Royce West said there would be no cover-up in the investigation, which other officials at the news conference said could take time.
Jailhouse video released earlier by the Waller County Sheriff's Department shows a space of about 90 minutes between the last physical check of Ms Bland in her cell and her being discovered dead at about 9am on 13 July.
The jail was decertified last Thursday because of problems with staff training and observing inmates.
Waller County Sheriff Glen Smith previously told Houston's KHOU TV that he did not think either problem played a role in Ms Bland's death.