By Joey Nolfi
April 16, 2018 at 04:15 PM EDT

Three years after Sandra Bland allegedly hung herself while in police custody, her family is questioning the circumstances surrounding her death in an exclusive clip from the upcoming HBO documentary Say Her Name: The Death and Life of Sandra Bland.

The footage (above) charts the Bland family’s journey to Waller County, Texas, where Sandra was found dead in her cell after an apparent suicide on July 13, 2015. Sandra was arrested three days prior for reportedly failing to signal a lane change. The arresting officer, Brian Encinia, approached Sandra’s car to issue a warning and subsequently forced her to get out of the car and placed her in handcuffs when she took issue with Encinia’s request that she put out her cigarette.

“We were told: ‘Once you get here, it will be proven, without a doubt. You’ll be able to see that she contributed in her own death,'” Bland’s mother, Geneva Reed-Veal, who filed a federal wrongful death lawsuit after Sandra’s death, explains in the clip. The family was then shown security tapes supposedly taken the day Sandra died, though what they saw only prompted more questions about the chain of events.

“The Texas Rangers, they walked us through footage…of the jail. We were looking, trying to see where Sandy was. I didn’t see her ever,” family attorney Cannon Lambert says as footage of normal prison operations from that day flashes onscreen.

“The video that we viewed when we went down [to Texas], it was only for the morning of Monday, July 13. There are no time stamps, there are no dates. Her cell was all the way at the back corner. She was in cell 95. The way they choose to phrase it is, ‘Where she was did not have cameras,'” Bland’s sister, Shavon, adds. “I think that’d be strange. Then how are you monitoring your inmates?”

“Why was she in a cell by herself? That’s a big cell for one person,” another of Bland’s siblings, Sharon Cooper, continues while medical staffers are seen wheeling a gurney down a hallway toward Sandra’s cell shortly after her body was found with a trash bag tied around the neck. “And when they were wheeling the gurney out, I went, ‘Whoa, she’s going to be on the gurney, right?’ Oh no… she was not on the gurney.”

The sneak peek is only the tip of the iceberg for Oscar-nominated Traffic Stop filmmakers Kate Davis and David Heilbroner, who helmed the project as a probing examination of the factors that contributed to Bland’s death. Issues of police brutality, racism, and systemic problems in America’s prison system all go under the microscope in Say Her Name, while law enforcement personnel with direct ties to the situation also appear on-camera in the documentary.

Say Her Name: The Death and Life of Sandra Bland, an HBO Documentary Films production, is set to world-premiere on Wednesday, April 25 as part of the 2018 Tribeca Film Festival. It will debut later this year on HBO, though an exact date has yet to be announced. Watch EW’s exclusive preview of the film (courtesy of HBO) above, and check out the movie’s key art below.