Actor Alec Baldwin accidentally shot and killed cinematographer Halyna Hutchins on Thursday after he discharged a prop firearm on the New Mexico set of "Rust." The film's director Joel Souza was also hit and injured but has since been released from the hospital. 

While the police are still investigating the fatal accident, many are left wondering how a prop firearm could leave someone dead and what type of safety protocols were in place to prevent this from happening.

Fox News spoke to experts in the props and weapons field about the incident. 

This accident is "an unprecedented procedural failure in the history of firearms safety. It's unbelievable," film and prop historian Michael Corrie told Fox News.

ALEC BALDWIN DISCHARGED PROP GUN THAT KILLED ‘RUST’ CREW MEMBER ON FILM SET: AUTHORITIES

"The person responsible for loading and ensuring that the firearm is ready for the scene is called an armorer [or weapons master], and you're supposed to have an armorer and an assistant armorer. Then there are several steps that you're supposed to go through to ensure that a weapon is loaded correctly with the correct type of blanks," Corrie explained. "Because there's more than one type of blank, there's lower power and then mid-power and then high-power blanks, and they create different visual effects."

Cinematographer Halyna Hutchins (L) was killed when Alec Baldwin (C) misfired a prop gun. Director Joel Souza (R) was also injured. (Photo by Fred Hayes/Getty Images for SAGindie  |  Jim Weber/Santa Fe New Mexican  |  Photo by Jim Spellman/Getty Images)

"Before the actor is even given the weapon, it's supposed to go through several stages of safety before it's handed to the actor. And the actor has to entrust that the armorer and everyone else involved have done their job correctly before handing the weapon to the actor," he continued. 

Armorer is a fairly new position in the history of film production, going back only to the 1980s. Before that, the prop master handled everything. Recently, it’s become more common to enlist specialists.

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The weapons master or armorer is required to be on set whenever a weapon is being used. The Actors' Equity Association's 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." Further, "All loading of firearms must be done by the property master, armorer or experienced persons working under their direct supervision."

Police arrived to the New Mexico set of "Rust" on Thursday after a woman was killed and a man was injured.  (NEWS NATION via KRQE)

A prop firearm could apply to anything from a rubber toy to a real firearm that can fire a projectile. However, if it's used for firing (even just blanks) it's considered a real gun.

A blank is a type of gun cartridge that contains gunpowder but no bullet. Still, it can seriously hurt or kill someone who is close by, according to the Actors' Equity Association. 

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It's still unclear what was shot out of the gun used by Baldwin on the set. The Santa Fe County Sheriff’s Office is investigating what "type of projectile was discharged."

Sean Matson, a retired Navy SEAL who has worked with the actors on the CBS drama "SEAL Team" in weapons handling, told Fox News, "The chain of custody is extremely serious [in regard to weapons on set]."

Production on "Rust" has been halted indefinitely.  (NEWS NATION via KRQE)

"You've got to teach people barrel discipline. I mean, things that you teach a basic person who is going to be using a firearm," Matson continued. "So any time someone hands me a weapon, even if they tell me it's unloaded, the first thing I do is I check to make sure it's unloaded. I'll pull out the magazine and get a visual check, day or night, to make sure that it is actually clear. And I know 100%, without a shadow of a doubt, I know the condition of that weapon. It's that critical."

Matson said on the procedural TV show there are retired SEALS on set to "assist and make sure that there's realism in the movement where their weapons are being pointed … just that extra level of scrutiny or checks in there is what helps."

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Stephen Gutowski, founder of The Reload, a firearms reporter and a gun-safety instructor, told Fox News, "Safety protocols on set were not followed. That's abundantly clear at this point. And I think that's the main takeaway of this whole situation is that guns — even prop guns — aren't toys. And if you're going to use them, especially in a professional capacity, like on a movie set, you need to be trained in how to use them, and you need to follow the safety rules that all times."

Both Hutchins and Souza were rushed to the hospital on Thursday evening. 

"Rust" is set in the 1880s, and Gutowski reasoned the production could be using a single-action revolver appropriate for the time period.

"They make replicas, and they still produce real, single-action revolvers today that are similar to those used in the period that this movie is supposed to take place in," he said. "It depends on what kind of gun they were using. But even if they were using a blank firing gun, you know, a prop gun designed to work with blanks. Specifically, there is a possibility that someone could have loaded a live round into that gun, and it could still propel that bullet projectile down and out the barrel towards somebody, even if it's not designed to do that necessarily."

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It remains unclear why Hutchins and Souza were in the line of fire, but it is fairly common to have a gun pointed at the camera and, by extension, the cinematographer, to get a certain angle.

"We’ve all seen the very famous shots in films where you get that dramatic effect of a gun being pointed at you, the audience, and of course, it’s being pointed towards the camera," Steven Hall told The Associated Press. Hall is a veteran second unit director and cinematographer who has worked on films like "Fury" and "Thor: The Dark World." 

Alec Baldwin released a statement on Twitter about the fatal shooting.  (Jim Weber/Santa Fe New Mexican  |  Twitter)

"To minimize that, one would put a remote camera in that place, or at least if someone does have to operate the camera, I’m normally protected by safety goggles, a safety visor and often a PERSPEX screen that withstands pretty much anything. Obviously, it wouldn’t withstand a real shot from a gun, but it would certainly withstand a blank."

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There has been an outpouring of dismay and anger from all levels of the industry that something like this happened. 

Director James Gunn tweeted that his greatest fear is that "someone will be fatally hurt on one of my sets." Actor Alex Winter tweeted that, "Crew should never be unsafe on set and when they are there is always a clearly definable reason why."

The Associated Press contributed to this report.