Gillian Laub found out about the segregated proms in 2002 when Anna Rich, then a high school student in Montgomery County, Georgia, wrote a letter to Spin asking them to cover the story. She couldn't bring her black boyfriend to the white prom, and she wanted the entire world to know about it.

Locals say the tradition of segregated dances dates back to the 1970s, and was put in place because the town didn't want the homecoming or prom queens to always be white, so they thought it made sense to elect two queens, which eventually led to having two proms. However, as time went on it became clear that it was more about avoiding interracial dating than making sure each race gets their own queen.

Laub responded to Rich's letter and went to Georgia. There she took photos of the students and met with some of their parents. The story ran in Spin, and Laub hoped that it would cause the town to take a long, hard look and make some crucial changes.

Five years later, Laub was in the Middle East, documenting the experiences of Jews and Palestinians after the second intifada, but her mind kept bringing her back to Montgomery County. "It's crazy that I can be halfway across the world and still haunted by images from my own country," Laub told MTV News over the phone.

When she returned from the Middle East, Laub called Mount Vernon High School to ask when their prom was. The receptionist on the other end didn't miss a beat and replied, "Which one?" And Laub knew she had to go back.

"I couldn't believe it," said Laub. "Obama is our President and they're still having segregated proms. I had to cover this."

When she arrived back in town, the locals remembered her, and they were not happy. Many parents of the students she had photographed for Spin were angry about the way she publicly shamed them for their tradition. She was threatened and told to leave, and even the cops said they couldn't protect her. In 2009, she published a story in New York Times Magazine, "A Prom Divided," which caused a loud enough outcry that that year, Montgomery County finally ended the tradition of segregated proms.

Laub thought her work in rural Georgia was complete, but then she received a phone call that changed everything.

Justin Patterson, a handsome 22-year-old black man, was shot and killed while running away from Norman Neesmith, a 66-year-old white man. "I realized how serious the situation actually was," said Laub. "On one hand we’re talking about mixing races, and sex, and then we're discussing a death."

So Laub returned to Georgia once again, and began filming what is now the HBO documentary, "Southern Rights."

When asked about the good things that came from telling this story, and the fact that young people want to have the complicated, necessary conversations about race, Laub was quick to give credit where it's due. "This all happened because one brave student wrote me a letter," Laub said. "If it weren't for these brave kids, the desegregated prom wouldn’t have happened."

She continued, "Nothing will bring Justin Patterson back. But the kids are excited to be part of the larger movement that's going on. And they finally feel heard."

“Southern Rites” premieres Monday, May 18 at 9 p.m. ET on on HBO.