The police investigation into a fatal shooting with a prop gun fired by actor Alec Baldwin on a film set was focusing Saturday on the specialist in charge of the weapon and the assistant director who handed it to Baldwin.

Ukraine-born cinematographer Halyna Hutchins, 42, was struck in the upper body and died shortly after the incident Thursday in New Mexico, while director Joel Souza, 48, who was standing behind her as they lined up a shot, was wounded and hospitalized, then released.

Police interviewed a visibly distraught Baldwin, who willingly cooperated, but have pressed no charges.

The incident stunned many in Hollywood and beyond, sparking intense speculation about how such an accident could have occurred despite elaborate gun-safety protocols for film sets.

The gun, which was supposed to be loaded with a blank charge, instead had a single live round, according to the affidavit submitted by the sheriff's office to obtain a search warrant, local media reported.

The affidavit said that Assistant Director Dave Halls, identified as the man who handed the gun to Baldwin during a rehearsal, called out "cold gun" as he did so -- industry code to indicate the weapon had only a blank charge. The court document said Halls was unaware the gun was actually loaded.

Police are focusing intently on the sequence of events that could have allowed a live round to be introduced to the set of the film, a 19th-century Western called "Rust."

A 911 call to police immediately after the shooting conveyed the shock and anger felt on the set.

"We've had two people accidentally shot by a prop gun; we need help immediately," the caller tells a police dispatcher.

"Was it loaded with a real bullet?" the dispatcher asks.

"I don't -- I can't tell you that," the caller replies. "And this (expletive) AD ... this mother (expletive) -- he's supposed to check the guns, he's responsible for what happens on the set."

Detailed gun safety guidelines from the Actors' Equity Association group specify that "all loading of firearms must be done by the property master, armorer or experienced persons working under their direct supervision."

The guidelines state: "Before each use, make sure the gun has been test-fired off stage and then ask to test fire it yourself. Watch the prop master check the cylinders and barrel to be sure no foreign object or dummy bullet has become lodged inside."

Baldwin, one of Hollywood's best-known actors, has said he was cooperating fully with the inquiry. He retweeted a story from trade journal Variety headlined "Alec Baldwin Was Told Prop Gun Was Safe Before Fatal Shooting, Affidavit Says."

The gun used, and two others, were provided by the film's weapons master, or armorer, who has been identified as 24-year-old Hannah Gutierrez-Reed, the daughter of longtime film-industry armorer Thell Reed.

In a September podcast, the young Gutierrez-Reed said she had some trepidation about serving as lead armorer for the first time for the previous movie she worked on, "The Old Way," another Western.

"I almost didn't take the job 'cause I wasn't sure if I was ready," she said on the "Voices of the West" podcast, before adding, "But doing it, like, it went really smoothly."

Halls and Gutierrez-Reed could not immediately be reached for comment.

District Attorney Mary Carmack-Altwies said in a statement Friday that the case is in its preliminary stages, adding, "At this time, we do not know if charges will be filed."

The Los Angeles Times, citing anonymous sources, reported that there had been at least three prop gun misfires prior to the fatal accident, and some crew members had protested working conditions.

It said at least one camera operator had messaged a production manager, saying, "We've now had 3 accidental discharges. This is super unsafe."

Rust Movie Productions said in a statement that it had not been made aware of any "official complaints" but would "continue to cooperate with the Santa Fe authorities."

It said it was also conducting an internal review.

"Rust," for which Baldwin is a co-producer, was being filmed in the foothills of northern New Mexico on sprawling Bonanza Creek Ranch, which has been used as the setting for scores of movies.

Baldwin stars as Harland Rust, an outlaw who goes on the run with his grandson after the latter is convicted of murder following an accidental killing.