The assistant director did not know the prop gun was loaded with live rounds, according to a search warrant filed in a Santa Fe court.
Cinematographer Halyna Hutchins was shot in the chest. Director Joel Souza, who was standing behind her, was wounded, the records show.
The warrant was obtained Friday so that investigators could document the scene at the ranch where the shooting took place. It notes that Baldwin's blood-stained costume for the Western film "Rust" was taken as evidence, as was the weapon that was fired.
Investigators also seized other prop guns and ammunition that were being used during shooting of the film starring Baldwin.
Earlier in the day, Baldwin described the killing as a "tragic accident." Baldwin was performing at the time of the shooting, the sheriff's office said. It was unclear how many rounds were fired, and little was known about the weapon.
"There are no words to convey my shock and sadness regarding the tragic accident that took the life of Halyna Hutchins, a wife, mother and deeply admired colleague of ours," Baldwin tweeted. "I'm fully cooperating with the police investigation to address how this tragedy occurred and I am in touch with her husband, offering my support to him and his family."
Baldwin continued, "My heart is broken for her husband, their son, and all who knew and loved Halyna."
1-— AlecBaldwin(HABF) (@AlecBaldwin) October 22, 2021
There are no words to convey my shock and sadness regarding the tragic accident that took the life of Halyna Hutchins, a wife, mother and deeply admired colleague of ours. I'm fully cooperating with the police investigation to address how this tragedy occurred and
2- I am in touch with her husband, offering my support to him and his family. My heart is broken for her husband, their son, and all who knew and loved Halyna.— AlecBaldwin(HABF) (@AlecBaldwin) October 22, 2021
Sheriff's spokesman Juan Rios said detectives were at the set Friday morning gathering evidence and information.
No immediate charges were filed, and Baldwin is permitted to travel, he said.
"He's a free man," Rios said.
Images of the 63-year-old actor - known for his roles in "30 Rock" and "The Hunt for Red October" and his impression of former President Donald Trump on "Saturday Night Live" - showed him distraught outside the sheriff's office on Thursday.
Guns used in making movies are sometimes real weapons that can fire either bullets or blanks, which are gunpowder charges that produce a flash and a bang but no deadly projectile. However, even blanks can eject hot gases and paper or plastic wadding from the barrel that can be lethal at close range. That proved to be the case in the death of an actor in 1984.
In another on-set accident in 1993, the actor Brandon Lee was killed after a bullet was left in a prop gun, and similar shootings have occurred involving stage weapons that were loaded with live rounds.
Gun-safety protocol on sets in the United States has improved since then, said Steven Hall, a veteran director of photography in Britain. But he said one of the riskiest positions to be in is behind the camera because that person is in the line of fire in scenes where an actor appears to point a gun at the audience.
Hutchins, 42, was airlifted to a hospital, where she was pronounced dead. Souza, 48, who was wounded in the collarbone area, was taken by ambulance to a medical center.
Sheriff's deputies responded about 2 p.m. to the movie set at the Bonanza Creek Ranch after 911 calls described a person being shot there, Rios said. The ranch has been used in dozens of films, including the recent Tom Hanks Western "News of the World."
"This investigation remains open and active," Rios said in a statement.
One of Hutchins' final social media posts was a photo of the "Rust" actors standing together in solidarity with crew members. She belonged to the IATSE union that represents crew members. The union is to vote soon on a new contract with producers after threatening to strike in recent weeks over issues including long hours and on-set safety.
Hutchins, a 2015 graduate of the American Film Institute, worked as director of photography on the 2020 action film "Archenemy" starring Joe Manganiello. She was named a "rising star" by American Cinematographer in 2019.
"I'm so sad about losing Halyna. And so infuriated that this could happen on a set," said "Archenemy" director Adam Egypt Mortimer on Twitter. "She was a brilliant talent who was absolutely committed to art and to film."
Manganiello called Hutchins "an incredible talent" and "a great person" on his Instagram account. He said he was lucky to have worked with her.
Hutchins had Ukrainian citizenship, according to Ukrainian Foreign Ministry spokesman Oleh Nikolenko. The country's consulate in San Francisco was working with U.S. law enforcement officials.
Baldwin teamed up as a producer with Souza on the 2019 film "Crown Vic," which starred Thomas Jane as a veteran Los Angeles police officer on a manhunt for two bank robbers. Souza's first credited film, 2010's "Hanna's Gold," was a treasure hunt adventure featuring Luke Perry.
After the shooting, production was halted on "Rust." The movie is about a 13-year-old boy who is left to fend for himself and his younger brother following the death of their parents in 1880s Kansas, according to the Internet Movie Database website. The teen goes on the run with his long-estranged grandfather (played by Baldwin) after the boy is sentenced to hang for the accidental killing of a local rancher.
Lee, son of martial arts star Bruce Lee, died in 1993 after being hit by a .44-caliber slug while filming a death scene for the movie "The Crow." The gun was supposed to have fired a blank, but an autopsy turned up a bullet lodged near his spine.
A Twitter account run by Lee's sister Shannon said: "Our hearts go out to the family of Halyna Hutchins and to Joel Souza and all involved in the incident on 'Rust.' No one should ever be killed by a gun on a film set. Period."
In 1984, actor Jon-Erik Hexum died after shooting himself in the head with a prop gun blank while pretending to play Russian roulette with a .44 Magnum on the set of the television series "Cover Up."
Such shootings have also happened during historical reenactments. In 2015, an actor staging a historical gunfight in Tombstone, Arizona, was shot and wounded with a live round during a show that was supposed to use blanks.
In Hill City, South Dakota, a tourist town that recreates an Old West experience, three spectators were wounded in 2011 when a re-enactor fired real bullets instead of blanks.
Berry reported from Phoenix. Associated Press writers Jake Coyle and Jocelyn Noveck in New York, Lizzie Knight in London, Yuras Karmanau in Kyiv, Ukraine, and Ryan Pearson in Los Angeles contributed to this report.