The call came the day after the world learned Sandra Bland’s name. Documentary filmmakers Kate Davis and David Heilbroner were at their summer cottage in Chilmark, closely following the news coming out of Texas about Sandra, an African-American woman who was found dead of an apparent suicide in a jail cell.

“We were on the Vineyard when the story broke,” said Mr. Heilbroner. “We were mesmerized by the story, and then the phone rings and it’s HBO. It’s one of those dream calls if you’re social issue filmmakers like us.”

In July 2015, Sandra Bland was taken into custody after a traffic stop in Prairie View, Tex. and placed in a cell in the Waller County jail. Three days later, she was found hanged in the cell. Her death was ruled a suicide, but the family and many others disputed the ruling, pointing to suspicious circumstances and alleging racial violence.

A week later, Mr. Heilbroner flew down to Texas to meet with the family. After gaining their trust, he and Ms. Davis switched on their cameras and began filming the two-year-long legal battle, culminating in the HBO documentary: Say Her Name: The Life and Death of Sandra Bland.

The film will be shown on Thursday, August 2 at the Film Center as part of Documentary Week. Ms. Davis and Mr. Heilbroner will participate in a discussion after the screening along with Sandra Bland’s sisters Shante Needham and Sharon Cooper, and lead attorney Cannon Lambert.

Say Her Name: The Life and Death of Sandra Bland.

Due to the nature of the case the filmmakers had to sign a nondisclosure agreement that would put them at financial risk should they leak any details. “The film was known at HBO as the unknown documentary,” said Mr. Heilbroner, who added that his background as a prosecutor is part of what drew him to the story. “Friends would ask us what we’re working on and we would just say a civil rights documentary.”

Mr. Heilbroner and Ms. Davis are no strangers to stories that delve into corruption and prejudice against minority groups. Their past work has focused on subjects ranging from the Stonewall riots to FBI entrapment in The Newburgh Sting, for which the couple won a Peabody Award.

The pair were also nominated for an Academy Award earlier this year for their short documentary Traffic Stop. The film followed an African-American teacher who was pulled over by a white police officer for a traffic violation that escalated into a violent arrest around the same time as Ms. Bland’s death.

“The story was very similar to Sandra Bland’s,” said Ms. Davis. “It was a much simpler story and faster to make, but we were intimately involved in issues of law enforcement, overreach and police brutality.”

Despite their years of experience, filming Say Her Name presented a host of challenges, the co-directors said, starting with how to conceive of a story that constantly revealed new twists and turns. They acknowledged that from day one of shooting, there was no assurance of how long they would have to be involved and whether a satisfying narrative would reveal itself.

“With documentaries, I go in with a plan and imagine a general structure and then have very specific questions in mind, and then when confronting reality it all goes out the window,” said Ms. Davis.

Mr. Heilbroner agreed, recalling a phrase a friend once told him about the storytelling process. “It’s like religion. You have to show up every day believing there’s a film. You have to believe you have a film that’s going to be worth watching and worth making.”

Luckily, they said, Sandra Bland left a record of social-justice themed videos that they were able to use in the film, giving viewers a glimpse of her strong-will and bubbly personality.

“What none of us could have predicted is that Sandra herself was such a singular person,” said Ms. Davis. “We were fortunate to be able to tell a story where there was so much material and people around her where we could humanize her. She’s not just a statistic.”

As new evidence was introduced and the filmmakers spent more time interviewing the family and members of law enforcement, even they began to doubt their assumptions about what happened. Actually, that’s the point of the film, according to Ms. Davis. She said she still believes that there could have been foul play involved, but acknowledged that her close view of the evidence, including a tour of the cell where Ms. Bland died, tempered her original notions of the case.

“It quietly asks viewers to look in a complex way at a situation that made people want to jump to conclusions,” she said. “I hope by the end people can get to a different kind of place that doesn’t let the system off the hook at all.”

“It doesn’t let any of us off the hook,” added Mr. Heilbroner.

Despite its heavy subject matter, the two said they wanted to end the film with a hopeful message, especially in the light of today’s frayed political climate. A scene toward the end of the film shows Sandra’s family gathered around her tombstone, not downcast, but dancing to the song Uptown Funk next to a large photograph of Sandra smiling.

“We really didn’t want the film to be a total downer,” said Mr. Heilbroner. “I hope people get to know Sandra Bland through the course of this film. For me, it was inspiring and so uplifting. She died under tragic circumstances but that doesn’t change the joy you get from getting to know her.”

He added: “Making this film in this particular political moment felt really important to me. This film is all about listening to each other, identifying within yourself the triggers and the prejudices that lurk within you and identifying them.”

Mr. Heilbroner said that Sandra’s sisters were in attendance for the film’s premiere, and told the audience afterward that the film made them feel like she was sitting next to them. That, he said, confirmed they were able to bring Sandra’s story to life in an authentic way.

Next up, the pair, along with Island-based producer Tamara Weiss, are taking on a lighter subject with Vineyard roots: rock music families. They said the film is called Born Into the Gig and will feature children of rock and roll icons, such as Ben and Sally Taylor, the son and daughter of James Taylor and Carly Simon.

“It’s nice to do something which is about something joyous,” said Mr. Heilbroner.

Say Her Name: The Life and Death of Sandra Bland will screen at 7:30 p.m. on Thursday, August 2 at the Film Center, as part of Documentary Week, which begins on July 30 and runs through August 4. Kate Davis and David Heilbroner will take part in a discussion along with Sandra Bland’s sisters Shante Needham and Sharon Cooper, and lead attorney Cannon Lambert. Visit for tickets and a full list of movies.