When Chris McCandless died alone in the Alaskan wilderness in an abandoned bus in 1992, his death was covered widely in the press. Jon Krakauer wrote a best-selling book about it, "Into the Wild," in 1996 (based on his Outside magazine article), which in turn led to a Sean Penn-directed film now in theaters.

When filmmaker Ron Lamothe heard the story, he was himself a recent college graduate, and he recalls how McCandless' story resonated with him. He thought it would make a good documentary: "I had myself just gotten back from a crazy trip through Africa, and we had gotten ourself in some situations that could be attributed to being 22," Lamothe said from his home in Massachusetts. "His story made sense to me. It was a tragic story, but as a figure, Chris appealed to me another way. ... He was a romantic figure as much as a tragic one."

After a "gestation period" of almost a decade, Lamothe began filming in Alaska in 2006, and has spent the past year editing. The film retraces McCandless' path through Alaska and contains some surprising revelations.

"I didn't set out to do an exposé; I never had any thought that I was doing an exposé," he says, "but what ended up happening was that the deeper I delved into the subject and story, I got into the minutiae and started discovering some things about the Krakauer book."

Lamothe's main contention is that McCandless died from anything other than starvation. "Into the Wild" suggests McCandless was poisoned by the seeds of a wild potato plant. Toxicology reports have disproved this, and Lamothe details the report by putting the man behind the forensic report onscreen.

Lamothe also does a caloric analysis of McCandless' final weeks, taken from his food log, and finds that he died around the time that his body mass index dropped below 14, which is generally thought to be the lowest sustainable number.

But perhaps the biggest scoop is Lamothe's discovery of the man who took McCandless' backpack from the bus. It has been said that McCandless gave all his money away and threw out his ID because he had a death wish. Lamothe debunks that myth by showing that his wallet had all of his identification cards as well as $300.

In the end, however, Lamothe isn't as interested in the details of McCandless' death as in showing what his story means emotionally - for the filmmaker as a young man and now that he's in his late 30s.

"Even before I set out, the story has slowly been changing. I think ultimately his symbolism matters to me most," Lamothe says. "I don't take the same kind of chances as I did when I was 22, which is good, but there is also a real sadness in that. Chris is forever suspended at 24. We all grow up and that's great, but there's less idealism and adventurism, more of an ambivalence."

2:30 p.m. Sat. and 2:45 p.m. Sun. $10.50. Part of the 6th San Francisco Documentary Film Fest. Check Web site for more festival information. Roxie Cinema, 3117 16th St., S.F. (415) 820-3907. www.sfindie.com.