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?