Lots of people in Austin have widely differing opinions about Brandon Darby, the former left-wing activist turned FBI informant and currently a favorite of the tea party.

Darby was the activist who informed on his fellow Austin comrades, David McKay and Bradley Crowder, who were arrested on domestic terrorism charges after homemade firebombs were discovered in a room where they were staying during the 2008 Republican National Convention in Minneapolis.

Darby didn’t cooperate with an earlier documentary, the award-winning “Better This World,” which looked into how the arrests affected the lives of McKay and Crowder. That documentary screened at South by Southwest a year ago. But Darby did work with Jamie Meltzer, the director of “Informant,” which will screen at 8:30 p.m. Sunday and 3 p.m. Wednesday at the Austin Film Festival.

Meltzer, who teaches documentary filmmaking at Stanford University, says he was drawn to the project after reading a story in The New York Times and wondered how someone who was a grass-roots community activist in New Orleans after Hurricane Katrina could end up being an informant.

“How does a guy go from radical activist to informant?” asks Meltzer. “It just brought up a whole bunch of questions, a series of questions that don’t have black and white answers. …. I wanted to explore the psychological story, as well as the ambiguities and complexities of the story.”

Shortly after learning of Darby’s odyssey in 2009, Meltzer says, he contacted the informant via email. “We didn’t do any interviews until four to six months later,” Meltzer says. But Meltzer says that it helped that he knew Michael May, the former managing editor of the Texas Observer, who was doing a “This American Life” piece looking at Darby’s personal, moral and psychological journey.

Still, it took a year before Darby agreed to let Meltzer use the interviews in the documentary. “I went a year without knowing whether I could make the documentary, partly because Brandon is very guarded. He has gone through a difficult time and was being attacked by everyone he had known.”

Meltzer uses multiple scenes of Darby at his home south of Austin, sometimes showing Darby as he works around his farm, sometimes showing him inside his home, cleaning a gun or setting the alarm system. Darby is also shown speaking to tea party events, warning them about possible violence from the American left. Some of the scenes, including a conversation between Darby and McKay about whether to use the homemade firebombs in Minnesota, are re-enactments. (In that scene, Darby is wearing a microphone, and an FBI agent is listening and taking notes, as occurred in real life.)

Yet there’s still a bit of murkiness as to why Darby did what he did. Darby tells Meltzer that he feared that McKay and Crowder might use the Molotov cocktails and kill someone. But others, including McKay, argue that they didn’t plan to hurt anyone but were considering whether to throw the homemade firebombs at a parking lot full of police cars. Darby’s detractors, many of whom are interviewed in “Informant,” also argue that Darby exaggerated the threat and was looking for attention.

Although Meltzer says he wanted to figure out Darby’s motivations, the director doesn’t come up with a definite answer. “I pushed … to find out more about his background,” Meltzer says. “He indicates some kind of abuse. He has a troubled family. He hints at these things. But I didn’t want to overemphasize those things (in the documentary). At the same time, I wanted to bring it up, to leave something in the back of your mind.”

Darby was a runaway in his late childhood, Meltzer says. “I think that caused him to go through a difficult period where he was very vulnerable on the street. That made him really aware of people who take advantage of other people. He connected in a big way with people being taken advantage of after Katrina. … Brandon is very guarded about his family history, and maybe there’s more there.”

Meltzer says he recently showed Darby a cut of the documentary. “He didn’t really like it,” Meltzer says. “He was torn about it. He thinks it contains arguments that he didn’t think were relevant.”

Meltzer says he sees “Informant” as independent of “Better This World” but a complement to it. “‘Informant’ is an open film,” he says. “It’s open to a lot of different interpretations. A lot of docs want to present a political argument about the world. Obviously, I had to make decisions. But I want people to make up their own minds. I don’t want to come down too harsh on anyone.”

(‘Informant’ screens at 8:30 p.m. Sunday at the IMAX Theatre at the Bob Bullock Texas State History Museum and at 3 p.m. Wednesday at the Hideout.)