Alec Baldwin isn't on trial for the fatal shooting of Halyna Hutchins anymore, but he’s clearly still upset over getting prosecuted over the "Rust" shooting tragedy... ‘cause he's now suing the prosecutors and investigators involved in his case.

The actor filed a lawsuit in New Mexico Thursday ... alleging prosecutors and investigators engaged in malicious prosecution, abuse of process, intentional spoliation of evidence, and violation of his civil rights.

Baldwin's side claims prosecutors became fixated on convicting Baldwin, regardless of the merits of the case ... and point to the shocking dismissal of the case in July to prove prosecutors acted improperly.

While he's filing this civil lawsuit for damages ... his lawyers explain no verdict in this case can ever undo the "trauma" caused by the State's threat of incarceration.

Baldwin named Special Prosecutor Kari Morrissey, Santa Fe District Attorney Mary Carmack-Altwies and investigators from the Santa Fe County sheriff’s office as defendants in the suit.

As you know ... on the set of "Rust" back in 2021, Baldwin was holding a gun that went off and killed Hutchins -- the movie's cinematographer.

Charges were filed against Baldwin earlier this year ... but, they were dismissed with prejudice when it was revealed prosecutors and investigators had filed some evidence under a different case number -- effectively hiding it from the defense.

The decision has been appealed multiple times ... though in December, the prosecutor's office gave up the appeal fight.

We've reached out to Morrissey, the Santa Fe District Attorney's office and the sheriff's office ... so far, no word back.