View of the Rust set at Bonanza Creek Ranch
View of the "Rust" movie set at Bonanza Creek Ranch near Santa Fe, New Mexico, U.S., January 20, 2023. Reuters

Cinematographer Halyna Hutchins was killed on the New Mexico set of Western movie "Rust" in 2021 after live ammunition was mixed with dummy rounds.

Actor Alec Baldwin fired the bullet that killed Hutchins and wounded director Joel Souza. Baldwin has said he is not responsible for Hutchins' death and pleaded not guilty to a charge of involuntary manslaughter in February.

Here's some details on what we know - and don't know.

WHO LOADED THE WEAPON THAT SHOT THE FATAL ROUND?

On Oct. 21, 2021, armorer Hannah Gutierrez-Reed, working as chief weapons handler on her second film, loaded a live round into a long Colt .45 revolver Baldwin was rehearsing with, believing it to be a dummy round.

Five other live rounds were later found on the set by investigators.

First Assistant Director Dave Halls said he checked the revolver with Gutierrez-Reed before it was handed to Baldwin. The actor fired the bullet as Hutchins directed him to point the weapon towards the camera.

Gutierrez-Reed is awaiting trial on criminal involuntary manslaughter charges. Her lawyer has said she will plead not guilty.

Halls has a March 31 hearing at which he is expected to plead guilty to a misdemeanor charge.

WHERE DID THE LIVE ROUNDS COME FROM?

Live rounds are not allowed on movie sets. Instead, guns are loaded with inert dummy rounds that look like live ammunition or blanks that make an explosive sound and muzzle flash when fired, or are left unloaded.

Investigators have not been able to establish where the live rounds found on the "Rust" set came from.

Gutierrez-Reed has said she brought two boxes of dummy rounds onto the set, as well as dummies loaded into gun belts from a previous movie production on which she worked, "The Old Way."

In a Nov. 9, 2021, police interview, Gutierrez-Reed said she loaded the live bullet that killed Hutchins from one of the two white cardboard boxes of dummy rounds she had brought onto the set.

But she said the tray of what were supposed to be dummy rounds inside the box - which police found contained other live rounds - could easily have come from another ammunition box.

WHERE DID THOSE TWO BOXES COME FROM?

In Dec. 7 testimony to New Mexico's worker safety bureau, Gutierrez-Reed said prop supplier Seth Kenney supplied her with the dummy rounds she used for the "The Old Way."

She said she then brought those rounds, in boxes and gun belts, onto the "Rust" set.

In January 2022 she sued Kenney, saying the ammunition she used was misrepresented as dummy rounds.

Kenney has denied that the live rounds on set came from his company. He has not been charged in the case.

WILL THIS EVER BE RESOLVED?

Charging documents held Gutierrez-Reed responsible for "allowing live ammunition on the set," but not for bringing them to the production.

Once the case reaches trial, defense teams for Gutierrez-Reed and Baldwin are expected to grill prosecutors over their inability to explain the source of the live rounds.

Without evidence Gutierrez-Reed and Baldwin knew of their possible presence on set it may be difficult for prosecutors to show they displayed a criminal level of negligence in Hutchins' death, legal experts say.