It sounds like you're referencing a release filename for the 2015 horror mockumentary Based on that, here’s a key feature of the film:

This unique format makes the final act especially powerful: the audience must piece together what happened solely through the protagonist’s black-and-white photos, which gradually reveal a terrifying, impossible truth.

, using only simulated "evidence" (photographs, news clips, police interrogation tapes, and talking-head interviews) to tell its story. There is no traditional live-action horror footage of the massacre itself—only the aftermath and the single roll of film a suspect took that night.