By Andrew Hay

(Reuters) - Alec Baldwin has informed a New Mexico state prosecutor and sheriff he may sue them after it emerged they withheld evidence from his defense team during their botched attempt to prosecute him over a fatal shooting on the movie set for "Rust."

A New Mexico judge dismissed involuntary manslaughter charges against Baldwin on the third day of trial on Friday, agreeing with his lawyers that prosecutor Kari Morrissey and the sheriff's office concealed evidence about the source of the live round that killed "Rust" cinematographer Halyna Hutchins in 2021.

Baldwin's lawyers sent letters to Morrissey and Santa Fe County Sheriff Adan Mendoza dated Monday asking them to preserve documents for future litigation, according to copies of the letters seen by Reuters.

Hutchins died when Baldwin pointed a gun at her as they set up a camera shot on a movie set near Santa Fe. The gun fired a live round inadvertently loaded by the movie's chief weapons handler Hannah Gutierrez. Gutierrez was convicted of involuntary manslaughter in March.

Gutierrez, serving an 18-month prison sentence, on Tuesday filed a motion for dismissal of charges due to the failure of prosecutors to disclose evidence on the live rounds, testing of Baldwin's gun by firearms expert Lucien Haag and an interview with the movie's props supplier Seth Kenney.

Erlinda Johnson resigned as Morrissey's assistant prosecuting the case on Friday, shortly before judge Mary Marlowe Sommer dismissed charges against Baldwin.

"As prosecutors we have obligations to disclose all the evidence," she said, adding that she believed it was right to dismiss the case. "We not only owe a duty to the people, but to the defendants accused of crimes as well."

Johnson said she did not give Baldwin's legal team details of the live rounds and only learned of that evidence when the defense did during testimony in court.