Video: Inside the 'controversial Mr Big' operation used to put NZ double murderer behind bars

For the first time ONE News can reveal details of the elaborate "Mr Big" operation that police used to secure the conviction of double murderer Kamal Reddy.

How police went undercover to catch Kamal Reddy - ONE News reporter Will Hine explains. Source: 1 NEWS

The technique, which was created by police in Canada, is controversial overseas and has resulted in overturned convictions.

Reddy was today sentenced to life in prison, with a minimum non-parole period of 21 years, for murdering Pakeeza Yusuf and her three-year-old daughter Juwairiyah Kalim.

He killed the pair in late 2006 and buried their bodies under a bridge, however police were not aware they were missing for six years.

Kamal Reddy murdered his partner and her young daughter and buried them under a bridge. Source: 1 NEWS

Once detectives began checking money records, they realised Reddy was their chief suspect.

By then the evidence trail had gone cold.

So, they put into play what is known internationally as a "Mr Big" sting.

It involved the creation of a fictitious crime organisation, which was made up of undercover officers.

Kamal Reddy was insistent in his denial that he did not murder Pakeeza Yusuf and Juwairiyah Kalim. Source: 1 NEWS

Reddy was lured into associating with the gang and carrying out activities he thought were criminal in nature, but in fact were elaborately mocked up by police.

These included counting large sums of money, handling drugs, receiving stolen goods, helping in a burglary, destroying supposed evidence from police investigations and helping police suspects evade capture.

More than 30 of these scenarios were staged over six months, with operations carried out in Kerikeri, Whangarei, Auckland, Tauranga, Thames, Rotorua, Hawkes Bay, Wellington, Picton and Tekapo.

They culminated in Reddy being introduced to the head of the crime family, "Mr Big", who told the organisation he was aware of a murder investigation in Reddy's past.

He was told to come clean, with the implication the gang would clean up any evidence and effectively make the crime go away.

First time the media has been allowed to publish details

Reddy initially denied the two murders, but then changed his story, telling Mr Big exactly how he carried out the killings.

He then took another undercover officer to the place he buried the bodies.

Kamal Reddy was convicted today of murdering Pakeeza Yusuf and three-year-old Juwairiyah Kalim and burying their bodies by a motorway. Source: 1 NEWS

Within days the remains had been excavated and Reddy was under arrest.

Mr Big tactics have been used seven times in New Zealand, but Reddy's case was the first that produced evidence put before a jury.

Today is the first time the media have been allowed to publish details of such an operation.

The Mr Big technique has been used extensively in Canada and Australia but is not permitted in countries that include Britain and the United States.

It is frequently criticised for putting the suspect under too much pressure and incentivising them to claim responsibility for a crime someone else might have committed.