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?

Go to this episode on rnz.co.nz for more details