“I’m grateful for the families that we’ve met, right? But I absolutely despise the terms that we’ve met under,” said Shante Needham. We were speaking three years after Needham lost her sister Sandra Bland—a 28-year-old black woman found dead in her prison cell while in police custody in Waller County, Texas, in 2015. Bland’s death, which occurred about a year after the Black Lives Matter movement became a national phenomenon, sparked protests. In the time since, Needham, who works in the medical field, and her sister Sharon Cooper, an H.R. professional, have both become activists, seeking justice for Bland (who they call Sandy), and meeting with families who have lost loved ones to police brutality.

“I’ve met women whose kids have been murdered, and they have yet to even get reports,” Needham continued in an interview at Vanity Fair’s New York office. “They have yet to even get the items that their loved ones had on them. So it’s challenging . . . But ultimately, I’m grateful for the solidarity. If we’re unified, then we can do so much more than when we’re divided.”

Cooper gave her sister an approving look. “Mic drop,” she declared.

In the HBO documentary Say Her Name: The Life and Death of Sandra Bland, premiering tonight at 10 P.M. Eastern time, Cooper and Needham revisit the traumatizing events surrounding Bland’s death and search for answers with directors Kate Davis and David Heilbroner. Three years ago, Bland was arrested in Waller County for an apparent traffic violation, jailed for three days, then found dead—hanging from a trash bag in her cell. Her death was ruled a suicide, but the public pushed back against that finding, not least because dashcam footage and a cell-phone recording from a bystander showed then-state trooper Brian Encinia forcefully arresting Bland and threatening to Taser her. Her story went viral, and her name became a rallying cry.

The documentary works twofold. It is, for the most part, a devastating true-crime examination, with Davis and Heilbroner analyzing every detail surrounding Bland’s death—from footage of her in jail to interviews with some of the Texas law-enforcement officials who handled her case.

“We did approach Officer Encinia and, not surprisingly, he refused to cooperate,” Davis said. “He was just off the map, I would say.” After Bland’s death, Encinia was charged with perjury, though the charge was later dropped when he agreed to leave the law-enforcement field. “A few people just disappeared,“ said Davis. “I think in the case of Encinia, his actions speak louder than his words.” The filmmakers also approached a guard who spoke to Bland shortly before her death, but he also refused to be in the film.

The documentary is also a deft portrait of Bland—a faithful churchgoer, a doting aunt, a black-history enthusiast, and a social-media activist who made about 60 video messages about her views on various social-justice issues. Thanks to all this footage, she also serves as a partial narrator for Say Her Name. “If I have one frustration, it’s that I couldn’t put more of her videos in the film,” Davis said.

Needham and Cooper are featured heavily in the doc, as is their mother, Geneva Reed-Veal, and family lawyer Cannon D. Lambert. Cooper said Lambert was fiercely protective of their family throughout the filmmaking process, which began five days after Bland’s death. HBO approached Davis and Heilbroner quickly, Davis says, largely because the married duo have made several films about social issues. Heilbroner met with the family and Lambert, who gave the green light shortly afterward.

The fact that Davis and Heilbroner are white did not give the family pause, said Cooper and Needham. “It’s not the color of the person; it’s the approach and the intent—what is your intent in doing this film? Is it to help, or is it to get an Oscar?” Needham pointed out, as Cooper approvingly snapped her fingers.

As is made obvious in the film, the sisters are perfect contrasts to one another; where Needham is quiet but direct, Cooper is peppy and extroverted, often snapping to emphasize her sister’s many mic-drop moments. They occasionally ribbed one another throughout our interview, especially when it came to a favorite topic: Cooper’s taste in music, which she shared with Bland.

“Sandy and I have eclectic musical taste compared to the rest of the family,” Cooper said with a laugh, referring to Needham and their two other sisters; she still calls herself “one of five” siblings. “Sandy and I were massive Maroon 5 fans.”

One of the last things she and Bland did together was see the band in concert on Bland’s 28th birthday. That memory reminded Cooper of a scene captured in the documentary, in which she and Needham visit Bland’s grave and blast Bruno Mars’s “Uptown Funk”—just because it’s “one of those songs she would have liked.”

“That’s a snippet into our intention to take back some of our joy, because it was snatched away,” she said. “It took me two and a half years to find a reason to smile again, and to be unapologetic about it.”

Years later, the sisters bristle at sayings like “time heals all wounds,” a platitude that seems divorced from reality. “It’s been three years,” Needham said of the grieving process. “It might take another 30 years! If you have not walked in these shoes, then you do not get a chance to tell me how long I should be grieving.”

As Say Her Name shows, there is still much that will never be known about Bland’s death. But her sisters remain devoted to activism, whether it’s by continuing to share Bland’s story, or providing support for families who have gone through similar tragedies in the public eye, despite the emotions the work can trigger.

“It’s not for the faint of heart,” Cooper said. “We’re dealing with it the best way we know how, which is one step at a time.”

Say Her Name airs on HBO on December 3 at 10 P.M. E.S.T.

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