And the fundamental, unanswered question of the film—whether a radical ideology can be made to fit the confines of mainstream society—is one that Green says he often wondered about.

“I grew up in the eighties and had idealistic impulses, but I looked around and it was a pretty bleak time,” he says. “I always wondered how the sixties became the eighties.”

The decade of Green’s youth, kicked off by the surrender of the Weather Underground’s remaining leaders to authorities in 1980, is represented in the film by starkly ironic images: clips from an aerobics video and footage of Ronald Reagan are juxtaposed with the rise of AIDS and crack cocaine.

Green says The Weather Underground began in earnest in 1998 out of “curiosity” springing from a series of conversations with a former activist living near him in San Francisco.

“I thought, ‘God, somebody should make a movie out of this,’” Green recalls.But as a director who had made only two previously-released films, the longest running 45 minutes, Green said he did not think himself up to the task at first.

“I tried to get a friend of mine who’s an established director, Mary Harron, to do it and I would help her,” Green says. “I really hadn’t done anything this ambitious.”

In 2000, Green says, he decided to go it alone, but he says the film faced financial challenges from the start.

“Getting grants to do a documentary about a group that tried to violently overthrow the U.S. government is not an easy thing,” he says.

And Green says the strong feelings still held by many on the film’s subject made it difficult to research—a process that meant not only hours combing through network news archives but also extensive in-person interviews with prominent figures from the would-be revolution.

“It’s obviously not the kind of story where you can go to the library, check out two books and know everything there is to know about it,” he says.

In one striking clip from The Weather Underground, activists bar journalists—“vultures,” in their words—from a leftist convention. The main characters of Green’s film spent ten years hiding from the world. And in a time when even the Weather Underground’s deathless bombings strike any number of deeply-felt chords, Green says he found that many of his subjects retained the same distrust of publicity.

“Initially everybody thought it was a bad idea,” he says. “Everyone we talked to said, ‘Don’t make this movie.’ Almost all the accounts of what happened had been very negative.”

Green says it was only after many months of off-record conversations that he and Siegel built up the trust of their subjects.

“His patience and diplomacy in dealing with these people was remarkable,” Subrin says. “It was a kind of Herculean task.”

Even after getting former Weathermen to speak with him on camera, Green says the interviews were far from easy.