The assistant director of the western film “Rust” grabbed a prop pistol from a gray cart and handed it to the movie’s star, Alec Baldwin, shouting “cold gun!” — which was supposed to indicate that it did not contain any live rounds, and was safe to handle around the crew huddled by the camera…

The assistant director “did not know live rounds were in the prop gun,” Detective Joel Cano wrote in the affidavit.

The weapon was “set up” on the tray by the movie’s weapons specialist, or armorer, along with a Western-style gun belt used in the scene. Detective Cano did not say what the armorer told investigators who arrived at the Bonanza Creek resort, where the film was shooting.

Ms. Hutchins, who was 42, was sitting in front of Mr. Souza, the director, watching the scene play out when the projectile struck her, the police said.