• Texas police accused of editing video before its release • Authorities say jail death being investigated in same way as murder case

Dashcam video from the officer who arrested Sandra Bland – a black woman who later died in Texas police custody – shows him threatening to drag her out of her car and “light her up” with a Taser after their encounter escalates from a routine traffic stop into an angry confrontation where she is forced to the ground and handcuffed.

The Texas public safety department released the footage on Tuesday amid continuing questions surrounding her arrest and subsequent death in a county jail. As the video circulated on Tuesday night, attention was being drawn to a number of abrupt breaks in what was thought to have been an original, uninterrupted recording – leaving the impression it had been edited before its release. A Texas department of public safety spokesman told the Guardian he did not have an immediate explanation as to why.

In the supplied video, trooper Brian Encinia’s police car, pulling away from an earlier traffic stop, does a U-turn and follows Bland’s car for about 30 seconds, stopping her after her car changes lanes to the right without signalling.

After telling Bland why she has been stopped, asking some questions and then walking away, apparently to complete paperwork or make inquiries, the officer returns.

“You seem very irritated,” he says at one point after returning.

“I am, I really am,” she replies, “because I feel like it’s crap is what I’m getting a ticket for, I was getting out of your way, you were speeding up, tailing me so I moved over and you stopped me so yeah, I am a little irritated but that doesn’t stop you from giving me a ticket, so.”

The stop escalates into an aggressive confrontation when Encinia asks her: “You mind putting out your cigarette please, if you don’t mind.” She replies: “I’m in my car, why do I have to put out my cigarette?” The officer tells her: “Well, you can step on out now.”

When she refuses, Encinia becomes irate and leans into her car, apparently trying to pull her out. “I’m going to yank you out of here,” he says. “I’m going to drag you out of here.” He pulls what appears to be a Taser out of a holster and shouts: “Get out of the car. I will light you up. Get out. Now.”

They then walk off camera. The officer tells her to put her phone down. “For a failure to signal! For a failure to signal!” she says. “You know this is straight bullshit … Oh I cannot wait until we go to court.”

A few seconds later they are briefly visible again and Bland’s wrists are behind her back. She is heard screaming and sobbing: “You’re about to break my wrist, stop! … You’re a real man now, you just slammed me, knocked my head into the ground, I got epilepsy, you motherfucker.”

Encinia replies: “Good.” Bland says: “You just slammed my head into the ground. Do you not even care about that? I can’t even hear.”

On Tuesday Texas politicians demanded transparency and state officials pledged a full and fair investigation after a meeting of elected representatives arranged amid continuing questions surrounding her arrest and subsequent death in a county jail.

“We want the Department of Justice, we want the FBI and every agency like it to look at it to make sure that no one in America can say this was whitewashed,” Royce West, a Texas state senator, said on Tuesday after a more than two-hour meeting at Prairie View A&M University, near where Bland was arrested and where she had been about to start a new job.

The Texas county where Sandra Bland died: there's 'racism from cradle to grave' Read more

“We want to make certain that there’s transparency. We know what’s going on in America,” he said, referring to the context of violent encounters across the country between African Americans and law enforcement.

“We believe there are questions that need to be answered as relates to the arrest,” West said. “She did not deserve to be placed in custody.”

Shortly after the press conference ended the Texas department of public safety (DPS) released the 52 minutes of dashcam footage of her arrest taken from the state trooper’s car.

“There’s a rush to judgment too often in America … but here in Texas I can tell you we believe in total transparency and we will find the truth wherever that leads,” said Dan Patrick, the state’s lieutenant governor. “We have to look at our procedures when people are taken into custody.”

The treatment of Bland at what had initially been a routine traffic stop and her death in custody three days later has sparked national outrage and widespread scepticism about the official account that she killed herself in her cell.

Encinia was placed on desk duty after the DPS said he violated traffic stop procedures and the department’s courtesy policy. “There’s no excuse for any instance where we don’t conduct traffic stops in a professional manner,” said Steven McCraw, the DPS director.

The 30-year-old became a trooper last year and previously worked as a firefighter and an ingredient processing supervisor at an ice cream factory, according to his LinkedIn profile.

He stopped Bland’s silver Hyundai Azera in Prairie View, near Houston, on the afternoon of 10 July, supposedly for failing to signal a lane change.

The Waller county district attorney’s office released Bland’s arrest warrant on Tuesday. Encinia writes: “I had Bland exit the vehicle to further conduct a safe traffic investigation. Bland became combative and unco-operative. Numerous commands were given to Bland ordering her to exit the vehicle. Bland was removed from the car but became more combative. Bland was placed in handcuffs for officer safety.

“Bland began swinging her elbows at me and then kicked my right shin. I had a pain in my right leg and suffered small cuts on my right hand. Force was then used to subdue Bland to the ground to which Bland continued to fight back. The 28-year-old was placed under arrest for Assault on Public Servant.”

Waller county officials released video from inside the jail on Monday after a news conference. It appears to show that no one entered her cell in the 90 minutes before her body was found, but there is no camera footage that shows the inside of the cell, according to the district attorney, Elton Mathis.

Facebook Twitter Pinterest The moments after Sandra Bland is found dead in a jail cell. Link to video

He said that it was too soon to make definitive conclusions as to whether her death was suicide or murder. Mathis pledged that the investigation would be carried out as thoroughly as if it were murder because “there are too many questions that need to be resolved”. The trash bag with which Bland allegedly hanged herself would be examined for DNA and fingerprints, he said, adding that her phone had been handed to the FBI to see if it contained any useful information.

“It has not been determined at this point that this is a murder,” he said on Tuesday. “Whenever you have a suspicious death, that is treated as a homicide.”

He said the results of the investigation would be presented to a grand jury that would decide if there is a criminal case to answer. West said that he had asked Mathis to ensure that the jury is ethnically diverse.

Waller county’s long history of racism and recent high-profile cases of fatal encounters between police and African Americans have seen the case gain attention on social media, especially given her family’s contention that there is no reason to believe she would take her own life. She had just driven from her home in Illinois to Texas to take up a job at Prairie View A&M University, her alma mater, and friends said she was in good spirits.

Activist groups have called for the US Justice Department to conduct an investigation. A media conference where LaVaughn Mosley, a friend of Bland, will demand Sheriff Smith’s resignation is scheduled for tomorrow.

A memorial service was held on the campus on Tuesday evening. Bland’s funeral is set for Saturday at a Chicago-area church, the Chicago Tribune reported.

“They will have justice in Texas,” Patrick said.