A lawyer for the armourer who oversaw weapons used on the Rust movie set has suggested that someone deliberately put a live round into the gun used by Alec Baldwin when he accidentally shot dead a cinematographer.

Jason Bowles said his client, Hannah Gutierrez, had pulled ammunition from a box that she believed contained only dummy rounds that were incapable of firing.

He said he thought it was possible that someone purposely placed real bullets, which look similar to dummies, into the box.

“We’re afraid that could have been what happened here, that somebody intended to sabotage this set with a live round intentionally placed in a box of dummies,” Mr Bowles said on ABC television’s Good Morning America.

“We’re not saying anybody had any intent there was going to be a tragedy of homicide,” he added, “but they wanted to do something to cause a safety incident on set. That’s what we believe happened”.

A spokeswoman for producers Rust Movie Productions had no comment on Mr Bowles’ remarks.

The company has said it is investigating the incident and had received no official complaints about safety on the set in Santa Fe, New Mexico.

Local authorities are investigating the matter and no charges have been filed against anyone involved.

Cinematographer Halyna Hutchins was killed on October 21 when a gun Baldwin was holding released a live bullet, police said.

Baldwin had been told by assistant director Dave Halls that the gun was “cold,” an industry term meaning it is safe to use.

Mr Bowles said Ms Gutierrez had checked the gun before giving it to Mr Halls.

She spun the cylinder and showed Mr Halls each of the rounds, which she believed were six dummy rounds, he said.

Mr Halls then took the gun into the church where Baldwin was rehearsing a scene.

Before the shooting, camera operators had quit the film to protest what they said were long hours and other objectionable working conditions, authorities in Santa Fe have said.

Asked who would intentionally place live ammunition with dummy rounds, Mr Bowles said on NBC’s Today show that he believed it could be a person who wanted “to prove a point, to say that they’re disgruntled, they’re unhappy”.

“And we know that people had already walked off the set the day before,” he said.

Baldwin, who was also a producer on the film, has said he is heartbroken and is co-operating with authorities.

On Tuesday, he shared a message on social media from a crew member who disputed reports of chaos and a lax attitude toward safety on the set.

-AAP