Is the Mr Big Sting: a powerful tool? Or an underhanded tactic? And can it bring justice?

The story's twists and turns continue. The defence team appeal, arguing again that the Mr Big sting evidence was unreliable and should not have been used.

This time the Court of Appeal agrees.

The defence lawyers go back to court to argue that there's not enough evidence now to convict David.

They win. The judge rules that David cannot be retried. He is free. The case is over.

Where does that leave Mr Big?

Should the law control Mr Big stings better? Is David Lyttle an innocent man tricked into telling a story that then he had to struggle for more than 10 years to escape? Or is he a murderer who crafted a story of innocence that eventually fooled the court?

And should the police use stories like Mr Big to try to get to the truth about a murder?

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The jury returns a verdict. Did they get it right?

The prosecution and defence close their cases with the stories they have gradually been revealing through the trial.

The prosecution lawyer emphasises David Lyttle's confession to the prison guards, his misleading statements about Brett's guns, the inadequately explained two-hour gap in his trip to the campsite.

The defence say it's all just a story David made up and most of it can't be true. And some drug dealers who killed Brett have gotten away with murder.

It's the job of the jurors to decide which side tells the most compelling story.

They return a verdict.

Did they get it right?

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Did the police push David Lyttle into a false confession? Or did they just give him an opportunity to tell the truth?

David Lyttle's defence lawyer wants the Mr Big confession gone.

He argues that is too unreliable - too obviously untrue - to be considered by the jury. What's more,the confession- and the whole case - should be thrown out because David Lyttle made it up in a desperate attempt to get into Mr Big's gang.

The judge isn't so sure.

Did the police push David Lyttle into a false confession? Or did they just give him an opportunity to tell the truth? Is it safe for the jury to rely on it?

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When the jury hear the Mr Big tapes, David's confession is held up to scrutiny.

The jury hears the detail of David's confession. How he did it. Why he did it. Where it happened.

And it turns out most of it is untrue. .

Defence lawyers say the seeds of David's confession were planted in the initial interviews, when police told David how they thought he did it.

The fakeness of David's "confession" hangs heavy.

Then, another bombshell. Suddenly there seems a lot less reason to doubt this confession.

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As doubts on both sides mount, the Mr Big evidence becomes crucial to the Crown's case.

David's story looks increasingly shaky. He can't immediately explain a two-hour gap on the morning he said he saw Brett. And he has repeatedly misled police during questioning.

The Crown is telling a powerful story about David's guilt.

But the defence story is starting to take shape too. It's surely enough to create reasonable doubt.

The Mr Big sting becomes crucial. Does it dispel that doubt?

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The Crown finally opens its case against David Lyttle.

After years of delays and postponements, the Crown finally opens its case against David Lyttle for the murder of Brett Hall.The contest of stories can finally begin.

What really happened? Will the rest of the evidence give us the full story?

And what will the jury think when they hear both sides?

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The trial begins, only to collapse after a week due to police failures. Can a fair trial ever happen?

The trial begins.

A week later, it's declared a mistrial. The Crown has just turned over evidence that seems to say someone saw the murder of Brett Hall - and the killer wasn't David Lyttle!

How could that possibly happen? It turns out that this is just the latest in an astonishing chain of disclosure failures by police investigating the case.

Is the justice system broken? Can a fair trial go ahead?

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We find it hard to believe people would confess to a crime they didn't commit. But they do.

What can psychologists tell us about Mr Big?

Leading experts in false confessions argue that we (and therefore jury members) find it difficult to believe that someone could confess to a crime they didn't commit, difficult to tell when someone is lying, and difficult to accept that it's people's predicaments that drive their behaviour, not their character.

All this makes David's lawyers nervous about the trial. They try put up expert evidence so the jury can understand these things, but the judges threw it out.They said juries should be able to understand all that on their own.

But can they?

Could you?

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The police get their confession. But can we believe it?

We go inside the sting police used on David Lyttle and look at the tactics involved: the nurturing of friendship with "Nick"; the offers of money, cars, trips and status.

David is told again and again the catchwords of the gang - truth, honesty, loyalty.

This is an organisation that looks after its people, that doesn't judge them, and that controls crooked cops who can fix anything.

As long as you are honest with Mr Big.

But is this fair? And can we believe any confession that comes from the sting?

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Only three countries in the world allow the Mr Big technique to be used. We're one of them.

Mr Big is a powerful technique that can bring justice to murder victims.

But experts disagree about its effectiveness.

Some support the technique. Others think Mr Big stings exploit people's vulnerabilities and encourage them to lie.

Not all countries use the sting, including the United States of America and the United Kingdom.

In Canada, police employ some surprising and troubling variations on Mr Big to get the accused to confess..

But despite all this, an undercover police team here in New Zealand get approval to run Mr Big on David Lyttle.

Will it work?

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Is this police sting reliable? Is it just?

When Halcombe builder David Lyttle answers a knock on his door in March 2014, he's drawn into a shadowy organisation with promises of wealth and friendship. David is desperate to join, but learns that first, he has to get the nod from the organisation's boss, Mr Big.

Mr Big asks David about his past. David says he's committed a murder. He shows the boss where he says the body parts are buried.

Then... he's arrested. It was all a police sting!

Police dig up the burial sites. There's nothing there.

Was this a confession?

Is it reliable?

Is it just?

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