August Underground(2001)

Overview:

Imagine walking down the street and finding an unmarked VHS tape. Curiosity piqued, you take it home and pop it in. What starts off as two men screwing around with a video camera quickly transforms into an ultra-realistic torture sequence where the unidentified psychopaths tape their exploits as they torment and violate a woman tied to a chair. The devastation of your morals continues throughout the entirety of the footage, while subtly revealing the killer's shattered pasts via the interaction with their victims and each other.