Not one cent has been paid out from police rewards of $170,000 offered in the past five years.
Last week, a reward of $50,000 was offered to whoever could finger the killer of Aucklander Jane Furlong.
Figures obtained under the Official Information Act reveal it is the fourth police reward offered since July 2008.
In 2009, two rewards were offered, $20,000 in relation to the disappearance of Tisha Lowry and $50,000 for the disappearance of Mallory Manning, both from Christchurch. A $50,000 reward for information which would lead to a conviction for the murder of Jordan Voudaris, a pizza shop owner in Paeroa, was offered last year.
Police would not confirm how much was paid but Herald on Sunday investigations found no money has changed hands.
A police spokesman said: "The decision to offer a reward, including the amount, must be agreed by the Commissioner of Police. Information received arising from a reward is subject to the same corroboration and scrutiny in court as any other evidence gathered during an investigation.
Furlong's body was found last year after she disappeared in 1993.
Detective Inspector Mark Benefield believed more than one person was involved in the murder, or at least held vital information.
He said Furlong's boyfriend Danny Norsworthy was a "significant person we believe could push this investigation forward but he has just declined" to help. People involved in court cases Furlong had been due to testify in were also refusing to speak to police.
The cases involved gang members accused of an assault and businessman Stephen Collie, charged with brutal attacks on sex workers.
Criminologist Greg Newbold said rewards were a sign of desperation and there was the risk of "mercenary" people giving false information. He believed Teina Pora was wrongfully convicted of the rape and murder of Susan Burdett in 1992. After police posted a reward of $20,000, Pora volunteered that he knew who committed the crime.
The two Mongrel Mob members he named were cleared by DNA tests and alibis - leading police to arrest Pora.
He was convicted by two juries but is seeking a royal prerogative of mercy from the Governor-General.
The detective in charge of the Tisha Lowry case, Virginia le Bas, said the murder conviction of her neighbour, Jason Paul Somerville, did not result from a reward.
Somerville confessed to the murder while being interviewed about the disappearance of his wife, Rebecca Chamberlain, 35, and both bodies were found under Somerville's Wainoni house.
He was sentenced to 23 years without parole.
The reward for information on Christchurch prostitute Mallory Manning, who was found in the Avon River, expired in 2010.
Mauha Huatahi Fawcett, 24, was arrested for the murder last year and a trial has been set for next month.
The reward for the Voudaris murder is being offered until July 1. Detective Sergeant Dean Anderson of the Matamata Piako CIB said it was a senseless killing. "We still have a reward in place for any material, information or evidence, which leads to the identity and conviction of any person or persons responsible for his murder," he said.