NEW YORK • More than a year before The Blair Witch Project hit theatres in 1999 and became a cultural phenomenon, its central mystery had already gone viral.
According to the movie's fledgling promotional website, which presented itself as a real investigative project, three film students - Heather, Mike and Josh - had ventured into the Maryland woods in 1994 to shoot a documentary and then disappeared.
Their footage was recovered a year later, providing evidence to support a disturbing legend. The online message boards began to buzz, with questions about the story's veracity.
The hype, intrigue and scepticism surrounding the account, fuelled by the Internet's advent, grew through the movie's premiere, in July 1999.
What eventually emerged - a feature-length film made of spliced-together scenes of shaky home-video footage - made the demise of its three characters seem all the more authentic and terrifying.
Of course, the whole thing was fiction. But a lot of viewers did not know that going in.
"The prime directive we had was that the film had to look completely real," said Eduardo Sanchez, who conceived and directed the entire thing with Daniel Myrick, from the manufactured legend to the film itself.
"The lighting had to make sense, the sound couldn't be great," he added. "There wasn't going to be a soundtrack. It was just edited footage."
Today, Blair Witch remains an inflection point for the movie industry.
Produced for US$60,000, the film went on to make US$248.6 million at the global box office, an indie record at the time.
Its amateur aesthetic prompted a generation of film-makers to pick up a camera, however low-tech.
It exposed new possibilities for marketing in the Internet age. And it was a ubiquitous part of pop culture, spawning myriad imitators and spoofs.
In the 20 years since Blair Witch's debut, the landscape has shifted profoundly.
The arrival of YouTube in 2005, which made video-sharing a global, social and economic enterprise, has deepened that blur.
Add to that the rise in reality television, fake news and phenomena such as "deepfakes", which use real images and voices to completely fabricate videos, and it becomes hard to imagine a hoax-based movie campaign ever again gaining that kind of currency.
Even the team that devised the original online strategy for Blair Witch recognises today that it passed through a narrow window.
"Now, it wouldn't work," Sanchez said. One could easily look to find out on the Internet that Heather from Blair Witch was an actress named Heather Donahue - who had not disappeared at all.
Still, few have matched that team's care and inventiveness since. The plan seems quaint in hindsight, but at the time, it was innovative.
First, Sanchez and Mike Monello, a producer on Blair Witch who was instrumental in funding and publicising the film, put together a stylistically unique website - filled with archival photos and a timeline of its purported history.
(The site is no longer online in its original form; www.blairwitch. com/project/main.html "is as close to the original site as you can get", Monello said.)
Then they monitored the site's message board, an early Internet outpost for horror fans to share theories and debate the so-called evidence. They started an e-mail newsletter for more loyal browsers and galvanised its hardcore fan base.
A week before the feature's wide release, Myrick and Sanchez debuted a separate faux documentary called The Curse Of The Blair Witch on the Sci Fi Channel (known today as SyFy). The Curse film was not presented as fiction.
That particular strategy may be hard to duplicate now, but the deeper lessons about connecting with fans in a media-driven age are still relevant.
"I think The Blair Witch Project was the first example of what the power of fandom would do in Hollywood," said Monello, now the founder of Campfire, an entertainment marketing agency.
"When you connect fans together on the Internet, their shared passion deepens."