THE LEAD DETECTIVE in the shooting of cinematographer Halyna Hutchins on the set of the film Rust is likely to be on the stand for most of Friday at Alec Baldwin’s involuntary manslaughter trial in New Mexico.

It comes as prosecutors try to cast the movie star as a reckless cavalier with a gun in his hand and the defence seeks to portray him as a working actor just doing his job.

Corporal Alexandria Hancock of the Santa Fe County Sheriff’s Office did not become the chief investigator until two weeks after the October 2021 shooting, but she conducted the first interviews of Mr Baldwin, Rust armourer Hannah Gutierrez-Reed and assistant director David Halls, the three people criminally charged in the case.

Ms Hancock was on the stand briefly at the end of the day on Thursday and will continue her direct examination by the prosecution on Friday before undergoing what is likely to be a long cross-examination by the defence as they look to poke holes in an investigation they have suggested unfairly focused on Baldwin.

Before Ms Hancock took the stand, Italian gunmaker Alessandro Pietta testified on Thursday about quality control in the manufacturing process for the gun eventually acquired by an Albuquerque-based gun and ammunition supplier to Rust and handled by Baldwin in the fatal shooting. It was shipped in 2017, and Mr Pietta last examined the gun in 2018 through a sales and distribution company.

The provenance of the gun, and its use for several years in trade shows, is under the microscope as defence lawyers raise concerns that the gun might have been modified or might otherwise be discharged under some circumstances without a trigger pull.

Baldwin has claimed the gun fired accidentally after he followed instructions to point it towards Ms Hutchins, who was behind the camera. Unaware that it was loaded with a live round, he said he pulled back the hammer — not the trigger — and it fired.

Both Mr Pietta and a sales distributor who handled the gun as recently as September 2021 testified that the revolver was in good working order and had not been modified.

Mr Pietta testified that the hammer on the gun would only drop with a trigger pull.

“If you want to release the hammer you have to pull the trigger,” he told the courtroom.

But Mr Pietta also noted that standard practice is to only load the gun – a remake of a 19th-century revolver – with five rounds and not six, to ensure the firing pin does not rest on a live round.

Gun experts including an FBI forensic expert acknowledge that the revolver can discharge if pressure is applied to the hammer while resting on a live round.

Before Ms Hancock returns to the stand, Judge Mary Marlowe Sommer will consider striking testimony from Thursday about a “good Samaritan” who walked into a sheriff’s station with what he told authorities was the supply of ammunition that the bullet that killed Ms Hutchins came from, after the conviction early this year of Gutierrez-Reed for involuntary manslaughter.

The issue came up during the defence questioning of the sheriff’s crime scene technician Marissa Poppell.

Baldwin’s lawyer Alex Spiro suggested with his questions that Ms Poppell and other authorities had been overly cosy with the film’s firearms supplier Seth Kenney and had insufficiently investigated whether he was responsible for the fatal ammunition reaching the set.

Mr Spiro asked Ms Poppell whether the “good Samaritan” had brought the ammunition into the sheriff’s department, and she said he had and she had written a report on it, denying that she had “buried it” to keep it from the defence.

Mr Spiro asked whether the man “told you you all had been duped by Seth Kenney”. Ms Poppell said she had no recollection of that.

The prosecution reacted with contempt for the suggestion that the man’s claims were legitimate.

Special prosecutor Kari Morrissey established in her questioning that the source of the ammunition was Troy Teske, a friend of Gutierrez-Reed’s father with motivations to redirect the blame, and despite similarities, the bullets were not the same size as the live rounds found on the Rust set, including the one that killed Ms Hutchins.

Ms Morrissey sought to further defend Mr Kenney’s role in her questioning of Ms Hancock.

“Did you ever discover any evidence throughout your entire investigation that Seth Kenney supplied live rounds to the set of Rust?” Ms Morrissey asked. Ms Hancock said no.

Mr Kenney has not been charged with any wrongdoing. An email sent to his lawyer seeking comment was not immediately returned.

Gutierrez-Reed’s lawyer said they have been informed prosecutors will try to call her to testify.

The lawyer, Jason Bowles, told The Associated Press in an email that Gutierrez-Reed will assert her Fifth Amendment rights against self-incrimination if she is called because she has an appeal of her conviction pending.

The judge declined to grant a pretrial request from prosecutors to give Gutierrez-Reed immunity for her testimony.

She is serving an 18-month sentence, the same penalty Mr Baldwin faces if he is convicted.