In 1997, when James Ronald Whitney, a broker at Tucker Anthony in New York, was speaking on the phone with screenwriter Jim Hart about a Broadway musical Whitney had written, Whitney's mom beeped in to tell him his grandmother was dying.

When Whitney clicked back to Hart, Whitney had a new idea. He thought a story about his incredibly dysfunctional family “would be amazing as a film.” But he needed to get information from his grandmother before she died.

Whitney doesn't waste time. “An hour and a half later, I had the treatment [of the film] done,” he says. “Later that day, I had booked flights, hotels and ordered film.”

What was the story? “When you grow up with a suicidal mother, you're constantly asking, ‘Why?’” he says. “I realized it had to do with [sexual] abuse by Melvin Just,” Whitney's grandfather. “He was abusing most of the family, and raped and murdered a social worker in front of three of them.”

In fact, Just, a junkyard mechanic in Carlotta, Calif., molested 10 of his children and stepchildren. Although the abuse was reported to authorities, Just was only charged with some of the crimes in 1978. “He was sentenced to 13 years and served eight,” Whitney says.

The social worker, Josephine Spegel, was sent to the Just home to help the children. She was strangled on March 10, 1969. “He killed her and got away with it,” Whitney says.

The case was reopened in the mid-90s, and Just took a polygraph. “Minus seven is lying. He was minus 16,” Whitney says. The detective tried to get the district attorney to bring him to trial, but Just suffered a stroke and his neurosurgeon wouldn't let the police interview him.

Since the courts had failed Whitney's family, he decided to try Just “in the court of public opinion,” he says. “When I started making the film, I promised the audience I wouldn't stop until he was in jail or dead.”

Whitney got his wish. On July 31, 1999, a few months after Whitney's last interview for the film, Just died.

Since its January 2000 premiere at the Sundance Film Festival, “Just, Melvin” has won best documentary at four film festivals in the United States and Canada. HBO bought the rights and will air the film Sunday, April 22.

Whitney was screenwriter, co-producer, co-executive producer, co-editor and co-music writer. On camera, Whitney confronts his grandfather about the molestation. Just denies the abuse. “At one point he threatened to molest me if I asked him any more questions,” he says. And although he was never physically abused by Just, Whitney openly reveals that an uncle molested him at age five.

Whitney pursued the film to bring attention to the horrors of child abuse. “I'm so proud of my family for having been as honest, open and courageous as they were,” he says. “They're so strong. They've gone through so much.”