The first film to screen at this year's Sundance Film Festival was a documentary -- director Mark Silver's and producer Gael Garcia Bernal's "Who Is Dayani Cristal?"

Screening off the beaten track at the Marc Theatre in the late afternoon, it may not have had a glamorous opening night vibe of "Crystal Fairy," which was unveiled three hours later at the larger Eccles Theatre -- but it officially kicked off a frigid Sundance 2013, and nobody who knows Sundance could argue that a non-fiction film shouldn't have gotten the leadoff spot.

For all of its reputation as a dealmakers' mecca and a launching pad for indies like the current Best Picture nominee "Beasts of the Southern Wild," Sundance has long been enormously rich in docs, both as a place to debut them and a place to develop them in the Sundance Institute's Documentary Film Program and fund.

In fact, in an introductory press conference on Thursday afternoon, fest founder Robert Redford pointed to Sundance's early championing of documentaries as one of its key elements.

Also read: 13 Movies You Have to See at Sundance [5]

The fest, now in its 29th year, is indeed a non-fiction powerhouse: Four of the five nominees in the Academy's current Best Documentary Feature category -- "Searching for Sugar Man," "The Invisible War," "5 Broken Cameras" and "How to Survive a Plague" -- debuted at last year's Sundance. And the only one that didn't, "The Gatekeepers," is in the program this year.

More impressively, 11 of the 15 films on the Oscar doc shortlist were Sundance entries.

The bar was raised pretty high for "Who Is Dayani Cristal?" After all, two docs played in the opening-night lineup last year: "Sugar Man," the closest thing to a favorite in the tightly contested Oscar race, and "The Queen of Versailles," the seventh-highest grossing doc of 2012.

Both of those were slick and entertaining; "Who Is Dayani Cristal?" is darker and tougher, a devastating look at the plight of undocumented workers told through a poignant single case study: The corpse of a man that was found in the Arizona desert, his only identifying mark a large tattoo that read "Dayani Cristal."

By the end of the movie we know the answer to the question the title poses, but the trip there is as powerful and graceful as the conclusion.

British director Silver delves into the U.S. medical examiners and Mexican officials who try against hope to identify the remains that have become more and more common in the last decade.

Overburdened by unidentified bodies that pile up at the rate of 200 a year in the Arizona desert, forensic anthropologist Bruce Anderson puts it bluntly: "The American people need to admit that it is to our benefit to have a blue-collar workforce with brown skins."

He also follows the story from the other end, revealing what we know about the man and what drove him to make 14 border crossings.

Bernal, meanwhile, makes a trip of his own through Central America and Mexico, retracing the man's steps as if he, too, were looking to enter the U.S. without documents.

The other travelers on that same road treat him like he's one of them, though the fact that he's a famous actor and he was accompanied by a camera crew no doubt meant that they were in on the whole thing.

Asked during a post-screening Q&A why the other men trying to sneak into the country were willing to be filmed, Bernal said it was simple: "They wanted to be on camera," he said. "They wanted their families to see what they were doing, because some of them might not make it."

And if "Who Is Dayani Cristal?" wades into a hot-button political issue, that's par for the course at Sundance. At the press conference, Redford also talked about the fact lots of the films at this year's fest, including "Lovelace," "Afternoon Delight," "Movie 43" and "Two Mothers," deal with sex.

The Utah-based public policy group the Sutherland Institute has blasted Sundance for that programming and asked the state government to pull its financial support of the festival if it shows sexually explicit material.

"Sometimes the narrowest mind barks the loudest," said Redford, "and we have come over time to just ignore it."