Alec Baldwin Must Have Pulled Trigger in 'Rust' Shooting, FBI Concludes

The FBI has concluded that Alec Baldwin must have fired the gun normally on the set of "Rust" -- which took Halyna Hutchins' life ... this according to a new report.

ABC News published a bombshell story Friday, claiming to have obtained a copy of the forensic analysis report recently completed by the Bureau ... which was examining all facets of the fatal accident in a broader investigation to see if criminal charges are warranted.

Per ABC, citing part of the FBI report, the feds found that the revolver in question -- a single-action .45 Colt caliber F.lli Pietta -- could not have been fired without someone pulling the trigger ... a determination they made after conducting accidental discharge testing.

Unclear if they did this testing with the same exact gun Alec used, or a separate but identical one -- but what the FBI notes in their reports is ... that gun, when working properly, will not release a bullet and primer simultaneously by just fiddling with the hammer alone.

That's what Alec said he was doing when the shooting occurred. You'll recall ... in a sit-down interview with ABC, he claimed all he'd done was pull the hammer back and pose it for the camera while Halyna coached him on positioning. When they were done, he released the hammer ... and says it fired without him pulling the trigger. The rest, of course, is history.

Well, that just doesn't make sense to FBI officials. Their report, per ABC, notes they set the hammer at varying angles and positions to see if they could make it fire without pulling the trigger ... but they say they couldn't. The only thing the hammer COULD do when de-cocked and then directly struck on its own (without pulling the trigger) was detonate the primer.

That essentially means it could set off the actual gunshot sound itself, without discharging a bullet, according to the FBI -- but that's obviously not what happened in AB's case.

Now, this conclusion doesn't necessarily mean Alec is in hot water quite yet -- again, we don't know if the testing they did here was with his gun or another ... it's totally possible the revolver he used that day did, in fact, malfunction and that he's telling the truth.

These findings have been sent off to law enforcement officials in New Mexico, who are still conducting their investigation dating back to October. One of the things they're still waiting on, per an official statement from the Santa Fe Sheriff's Office, is phone records from Alec.