Alec Baldwin's defense team filed a motion alleging the prosecution of hiding ammunition evidence, which resulted in the dismissal of his involuntary manslaughter charge.

The actor sobbed and hugged his attorneys as the judge threw out the case due to errors made by the police and prosecution after an incredible day in court during which the special prosecutor called herself as a witness.

The 66-year-old Baldwin has consistently refuted the accusation of involuntary manslaughter in connection with the shooting death of cameraman Halyna Hutchins. He argues that others on the Rust filming set in New Mexico were in charge of making sure the pistol was safe.

He faced up to 18 months in prison if he had been convicted.

According to the prosecution, the star had behaved recklessly during a scene rehearsal on the set near Santa Fe, playing "make believe with a real gun" and violating "the cardinal rules of firearm safety". But the defence team argued this was not true - he was "an actor, acting" and "committed no crime".

Now, almost three years on from Ms Hutchins' death, the case against Baldwin has been dismissed - and Judge Mary Marlowe Sommer has said it cannot be filed again.

"The late discovery of this evidence during trial has impeded the effective use of evidence in such a way that it has impacted the fundamental fairness of the proceedings," the judge said.

His wife Hilaria, who was supporting him in court throughout the trial along with his actor brother Stephen, also cried as the judge made the ruling. Baldwin left the building shortly afterwards and got straight into a car, without speaking to reporters outside.

The breakdown of the case began following the second day of evidence, during which the actor's defence team learned the Santa Fe sheriff's office had taken possession of live rounds as potential evidence earlier this year, on the same day the film's armourer, Hannah Gutierrez, was convicted of involuntary manslaughter for her role in Ms Hutchins' death.

Investigators did not list these live rounds in the Rust file, nor were they disclosed to defence lawyers. Prosecutors said the ammunition was not connected to the case and was not hidden.

The Colt 45 rounds at the centre of the dismissal were handed in by Troy Teske, a friend of Gutierrez's stepfather Thell Reed.

Baldwin's legal team filed their request to dismiss overnight, and the court heard arguments on the motion from both parties without jurors present in the courtroom.

Ms Morrissey said the bullets were not the same size or chemical composition as the live rounds found on the Rust set, including the one that killed Ms Hutchins. "This is a wild goose chase that has no evidentiary value whatsoever," she said. "This is just a man trying to protect his daughter."

When Judge Marlowe Sommer decided she needed to hear more evidence to make a decision on the motion, she called the jurors in only to dismiss them straight away.

The court then heard evidence from witnesses including prop store owner Seth Kenney, who provided blanks and dummy rounds to the set of Rust. He has denied supplying live ammunition to the production and has not been charged in the case. Corporal Alexandria Hancock and Lieutenant Ryan Randall, from the Santa Fe County Sheriff's Office, also testified.

Following the repeated suggestions from defence lawyer Alex Spiro that evidence had been concealed, in an unusual move, special prosecutor Kari Morrissey called herself to the witness stand, despite the judge telling her she was not required to do so.

She denied evidence had been hidden and maintained she had felt it was not relevant.

But Judge Marlowe Sommer found the prosecution's conduct was "highly prejudicial" to Baldwin and there was "no way for the court to right this wrong".

During his questioning, Mr Spiro put it to Ms Morrissey that she simply did not "like Mr Baldwin very much".

"That is absolutely untrue," she replied. "I actually really appreciate Mr Baldwin's movies. I really appreciated the acting that he did on Saturday Night Live, and I really appreciate his politics."

Mr Spiro told the court that she had referred to the actor as a "c*********" and an "arrogant p****" to witnesses. She said she did not recall this.

During questioning, it also emerged that another prosecutor, Erlinda Johnson, had resigned from the case earlier that day.