Gun in 'Rust' shooting could not have been fired without pulling trigger: FBI report

The gun used in the fatal shooting on the "Rust" movie set could not have been fired without pulling the trigger, according to an FBI forensic report obtained Friday by ABC News.

Actor Alec Baldwin shot cinematographer Halyna Hutchins on the set of the Western, which he was producing and starring in, last year. The actor believed he was handling a "cold gun" -- one without live ammunition -- when it went off and a live bullet struck Hutchins, killing her. The film's director, Joel Souza, was also wounded in the shooting.

Accidental discharge testing determined that the firearm used in the shooting -- a .45 Colt (.45 Long Colt) caliber F.lli Pietta single-action revolver -- could not have fired without the trigger being pulled, the FBI report shows.

With the hammer in the quarter- and half-cock positions, the gun "could not be made to fire without a pull of the trigger," the report stated.

With the hammer fully cocked, the gun "could not be made to fire without a pull of the trigger while the working internal components were intact and functional," the report stated.

With the hammer de-cocked on a loaded chamber, the gun was able to detonate a primer "without a pull of the trigger when the hammer was struck directly," which is normal for this type of revolver, the report stated.

In an interview with ABC's George Stephanopoulos in December, Baldwin said he didn't pull the trigger on the gun.

"The trigger wasn't pulled," he said. "I didn't pull the trigger."

ABC News reached out to representatives for Baldwin and Hannah Gutierrez Reed, who was in charge of all weapons on the "Rust" set, but did not receive a response as of yet.

The forensic report is part of a criminal investigation into the on-set shooting. The Santa Fe County Sheriff's Office, which is leading the homicide investigation, received the report and other FBI documents related to the shooting earlier this month, the sheriff's office said Thursday.

The documents have been reviewed by the New Mexico Office of the Medical Investigator, which has classified Hutchins' death as an accident, a postmortem report obtained by ABC News shows.

"Death was caused by a gunshot wound of the chest. Review of available law enforcement reports showed no compelling demonstration that the firearm was intentionally loaded with live ammunition on set," the report stated. "Based on all available information, including the absence of obvious intent to cause harm or death, the manner of death is best classified as accident."

The local district attorney has yet to make any charging decisions in the case. Detectives are awaiting phone records from Baldwin as part of their investigation, the sheriff's office said Thursday.