A new documentary premiering at SXSW reveals fresh evidence that the infamous 1967 Patterson-Gimlin Bigfoot film was an elaborate hoax. The film, which shows a man in costume moving through the woods, appears to be a dress rehearsal for the later footage that became a cornerstone of cryptid lore.

Roger Patterson's son Clint Patterson, who was 12 when his father died in 1972, confirms the family secret in the documentary. He recalls his father's evasive behavior when claiming they'd captured Bigfoot on film, describing it as a lifelong "chip on my shoulder" that led to family estrangement when he tried to expose the truth.

The documentary's director Marq Evans obtained the rehearsal footage from a Kodak reel dating to 1966, discovered in a safe at Olympic College. The reel shows Patterson's brother-in-law in costume moving in a similar manner to the 1967 footage, though with a different location and a larger actor.