The Legal Question at the Center of the Alec Baldwin Criminal Case

Now that a grand jury has indicted Alec Baldwin on a charge of involuntary manslaughter for the fatal shooting of a cinematographer on the set of the film “Rust” in New Mexico in 2021, the contours of the looming legal battle are coming into focus.

If the case reaches trial, the challenge prosecutors face will be convincing a jury that Mr. Baldwin was guilty of either the negligent use of a firearm or of acting with “total disregard or indifference for the safety of others” — even though investigators found he was told on the day of the shooting that the gun he was rehearsing with contained no live rounds, and even though the film set was not supposed to have any live ammunition at all.

The challenge Mr. Baldwin’s defense team faces will be to explain why the gun fired. Mr. Baldwin has maintained all along that he did not pull the trigger that day as he rehearsed a scene in which he draws a revolver, saying that the gun discharged after he pulled the hammer back and released it. A forensic report commissioned by the prosecution determined that he must have pulled the trigger for the gun to go off, a finding that contributed to its decision to revive the criminal case against Mr. Baldwin.

Legal experts were divided on the merits of reviving the case, noting that traditional gun safety rules — such as never pointing a functional gun toward someone — do not always apply on film sets, and that investigators found he had been assured by the film’s safety crew that the gun did not contain live ammunition.

“The notion that you never point a gun at someone would sort of undo westerns for the past 100 years,” said Nancy Gertner, a retired federal judge.

The outcome of the case at trial — the State of New Mexico vs. Alexander (Alec) Rae Baldwin — would hinge on how jurors view two key questions: Should Mr. Baldwin have known of the danger involved in his actions that day? And, using a term of art in criminal law, did he act with a “willful disregard for the safety of others”?

The grand jury indictment required that at least eight out of 12 jurors found probable cause that Mr. Baldwin committed a crime. The standard at trial is much higher: A jury must determine, unanimously, that he is guilty beyond a reasonable doubt.

“I think it’s an uphill battle,” said Steve Aarons, a veteran defense lawyer in New Mexico. “There is no reason for live rounds to be there. It’s a little different than other situations where you have a firearm and you assume any bullet that is there would be a live round.”

There is a complex web of factors that would quite likely come up at trial, including the condition of the gun, which broke during F.B.I. testing, and Mr. Baldwin’s responsibility as a producer on the film.

(Mr. Baldwin has asserted that even though he was a producer, he had no involvement in hiring crew members, including the movie’s armorer, Hannah Gutierrez-Reed, who was responsible for guns and ammunition on the set. She has pleaded not guilty in the involuntary manslaughter case against her.)

But the prosecutors will probably take the straightforward position that anyone who agrees to handle a gun is responsible for what happens next, said Joshua Kastenberg, a criminal law professor at the University of New Mexico and a former prosecutor.

“You could make the argument that regardless of the condition of the weapon, there was an independent duty of every person that was going to put their hands on that weapon that day to ask and make sure that it was either safe or unloaded,” he said, though he said that proving that kind of argument to a jury is often challenging.

After the grand jury indicted Mr. Baldwin on Friday, his lawyers — who have called the revived prosecution “misguided” — said that they looked forward to their day in court. Kari T. Morrissey, one of the special prosecutors handling the case, declined to elaborate on the case that was presented to the grand jury.

It was the second time Mr. Baldwin found himself facing a criminal charge in connection with the shooting. In an earlier case that was dropped in April, prosecutors had accused him of “extremely reckless acts” in the shooting. In a statement of probable cause last year they had accused him of getting insufficient firearms training, of failing to deal with safety complaints on set in his capacity as one of the film’s producers, of “putting his finger on the trigger of a real firearm when a replica or rubber gun should have been used” and of pointing the firearm at the film’s cinematographer and director.

Mr. Baldwin has maintained all along that he was not responsible for the tragedy, noting that someone else had put live ammunition in the gun and that the cinematographer, Halyna Hutchins, had been directing where he pointed the gun. “I know in my heart that I’m not responsible for what happened to her,” Mr. Baldwin told a detective following the shooting.

The new case, said Marc A. Grano, a lawyer and former prosecutor in New Mexico, will most likely become a back and forth over what is “standard practice” in the film and TV industry, a battle that may include conflicting opinions and examples.

After the original criminal case was brought against Mr. Baldwin last year, SAG-AFTRA, the union representing film and TV actors, opposed the prosecutors’ contention that actors were responsible for ensuring that the guns they were handed on set were safe to handle, saying, “an actor’s job is not to be a firearms or weapons expert.”

The most widely used written protocols around gun use on sets are outlined in documents called Safety Bulletins No. 1 and No. 2, which were created by a team of representatives from the unions and the major studios, and which will most likely be used as evidence in court.

The fatal shooting of Ms. Hutchins prompted the first revisions to those safety guidelines in two decades. The new guidelines, published in December, are longer and more detailed than the old ones, and stress that safety meetings should include instructions on how to distinguish between blank ammunition, which have gunpowder but not projectiles, and dummy rounds, which are inert and cannot be fired.

As before, they make it clear that live ammunition is not supposed to be used on sets. “Live ammunition,” the bulletin says, “is never to be used on set nor brought onto any work location, including any studio lot, stage or location” except in rare cases if it meets specific exceptions.