"The trio behind the monitor began repositioning the camera to remove a shadow, and Baldwin began explaining to the crew how he planned to draw the firearm. He said, "So, I guess I'm gonna take this out, pull it, and go, 'Bang!'" When he removed it from the holster, the revolver discharged a single time. Baldwin denied pulling the trigger of the gun, while ABC News described a later FBI report stating that the gun could only fire if the trigger was pulled. Halls was quoted by his attorney Lisa Torraco as saying that Baldwin did not pull the trigger, and that Baldwin's finger was never within the trigger guard during the incident. When the gun fired, the projectile traveled towards the three behind the monitor. It struck Hutchins in the chest, traveled through her body, and then hit Souza in the shoulder. Script supervisor Mamie Mitchell called 9-1-1 at 1:46 p.m. PT and emergency crews appeared three minutes later. Footage of the incident was not recorded."

"In August 2022, FBI forensic testing and investigation of the firearm determined the Pietta .45 Long Colt Single Action Army revolver could not have been fired without a trigger pull from a quarter cocked, half-cocked, or fully cocked hammer position. It was also determined that the internal components of the revolver were intact and functional which ruled out mechanical failure as a reason for an accidental discharge. Baldwin stated during a December 2021 interview for ABC News that "the trigger wasn't pulled" and "I didn't pull the trigger."

So he most likely lied about it. Maybe he was drunk or on drugs..

"On January 19, 2023, New Mexico First Judicial District Attorney Mary Carmack-Altwies said she would charge Baldwin and Gutierrez-Reed with two counts each of involuntary manslaughter. Halls agreed to plead guilty to negligent use of a deadly weapon, and received a suspended sentence and six months of probation."

"On June 22, 2023, Gutierrez-Reed faced a second charge of tampering with evidence, in which the special prosecutors allege that she transferred "narcotics to another person with the intent to prevent the apprehension, prosecution or conviction of herself.” They later specify from a June 29 court filing that she attempted to conceal a small bag of cocaine the night of the fatal shooting after her initial police interview. On August 4, 2023, Gutierrez-Reed waived her right to a preliminary hearing to determine whether or not the criminal charges would stand, thus allowing the trial to move forward and on August 9, she pleaded not guilty to both charges. On August 21, a New Mexico judge scheduled her trial to run February 21 through March 6, 2024."

There were drugs on set.

"On November 10, Rust gaffer Serge Svetnoy filed a lawsuit against the production for general negligence. A second lawsuit was filed on November 17 by script supervisor Mamie Mitchell, who says the script did not call for the discharging of a firearm. On January 23, 2022, Baldwin and other producers filed a memorandum that asked a California judge to dismiss the November 17, 2021 lawsuit by Mitchell. In November 2022, the court rejected a request to dismiss Mitchell's lawsuit against Baldwin and his production company"

I didn't know it is his own company as well..