Alec Baldwin’s defense attorneys argued Monday that damage done during FBI testing to a revolver that killed a cinematographer on the set of the Western “Rust” has stripped them of the ability to put on a proper defense at the actor’s forthcoming trial, and asked a New Mexico judge to dismiss the involuntary manslaughter charge against him.

“They understood that this was potentially exculpatory evidence and they destroyed it anyway,” Baldwin lawyer John Bash said during a virtual court hearing. “It’s outrageous and it requires dismissal.”

Prosecutors argued that the gun breaking into pieces during testing was “unfortunate” but that Baldwin’s team still has plenty of evidence for a defense and did not meet their burden for having the case thrown out.

Judge Mary Marlowe Sommer said she expects to issue a ruling on the motion to dismiss on Friday.

During the fatal rehearsal on Oct. 21, 2021, Baldwin was pointing the gun at Halyna Hutchins on a movie-set ranch when it went off, killing her and wounding director Joel Souza, who survived.

Sheriff’s investigators initially sent the revolver to the FBI only for DNA testing, but when an FBI analyst heard Baldwin say in an ABC TV interview in December that he never pulled the trigger, the agency told the local authorities they could conduct an accidental discharge test.

The FBI was told to go ahead, and tested the revolver by striking it from several angles with a rawhide mallet. One of those strikes caused the gun to break into three pieces.

The FBI had made police and prosecutors aware that the test could do major damage to the gun, which hadn’t been tested by the defense, but the authorities went ahead with the test without bothering to disassemble it and photograph its parts first, thus eliminating their most critical evidence in the case, Baldwin’s lawyers argued.

“We can never use our own expert to examine that firearm,” Bash said.

The prosecution argued that the gun was not destroyed as the defense said.

“The parts are still available,” special prosecutor Erlinda Johnson said. “The fact that this gun was unfortunately damaged does not deprive the defendant of ability to question the evidence.”

But Baldwin’s lawyers said the damage done to the top notch on the revolver’s hammer rendered the most important testing impossible.

They argued that if Marlowe Sommer declined to throw out the case, she should at least not allow any of the technical gun analysis to be presented at trial.

Baldwin’s attorneys gave long and probing cross-examinations to the lead detective, an FBI forensic firearm investigator and the prosecution’s independent gun expert in testimony that was likely a dress rehearsal for the high profile trial, where Baldwin, who was not on the online hearing, will be appearing in person.

The special prosecutors running the case argued that those cross-examinations proved that the defense has plenty of gun evidence to work with at the trial.

“They have other reasonable available means to making their point,” Johnson said.

She added that all available evidence, from witness testimony to video of Baldwin firing the gun in movie footage, showed that the gun was in good working order on the day of the shooting, and that police had no reason to believe its internal workings could provide exonerating evidence.

Prosecutors plan to present evidence at trial that they say shows the firearm “could not have fired absent a pull of the trigger” and was working properly before the shooting.

Defense attorneys are highlighting a previously undisclosed expert analysis that outlines uncertainty about the origin of toolmarks on the gun’s firing mechanism.

Baldwin has pleaded not guilty to the involuntary manslaughter charge, which carries a maximum sentence of 18 months in prison.

Armorer Hannah Gutierrez-Reed was convicted in March of involuntary manslaughter for her role in the shooting and was sentenced to 18 months in prison.

On Friday, the judge denied prosecutors’ request to use immunity to compel testimony from Gutierrez-Reed at Baldwin’s trial. Her statements to investigators and workplace safety regulators will likely feature prominently in Baldwin’s trial.

Last year, special prosecutors dismissed an involuntary manslaughter charge against Baldwin, saying they were informed the gun might have been modified before the shooting and malfunctioned. But they pivoted after receiving a new analysis of the gun and successfully pursued a grand jury indictment.