After an extraordinary day in court - during which the special prosecutor called herself as a witness - the actor broke down in tears and hugged his lawyers as the judge made the ruling and threw out the case, based on mistakes by police and prosecutors.

Baldwin, 66, had always denied the charge of involuntary manslaughter over the fatal shooting of cinematographer Halyna Hutchins, maintaining he did not pull the gun's trigger and that others on the set of the Western film Rust, in New Mexico, were responsible for safety checks on the weapon.

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.

Read more:
Rust to be shared 'with the world': What's next for Alec Baldwin?

"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.

How the case collapsed

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.

Prosecutor calls herself to the stand

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.

Read more from Sky News:
The A-list guestlist at son of Asia's richest man's wedding
Holly Willoughby plotter Gavin Plumb jailed
Ryan Reynolds teams up with best friend Hugh Jackman

Following the judge's ruling, Gutierrez's lawyer Jason Bowles told Sky News the judge had done "the right thing to preserve the integrity of our system".

Gutierrez was sentenced to 18 months in prison and is currently appealing. Mr Bowles said they would now be filing a "similar motion" in her case.

There has still not been a definitive determination on how the live rounds made their way on to the film set.

Baldwin, who is known for films included The Departed, It's Complicated and The Hunt For Red October, as well as his performances on Saturday Night Live, can now put the case behind him. He has a film, Clear Cut, out next week, and is set to star in a reality TV series next year.