A "chilling" TV series using psychics to shed new light on murder cold cases has been ice-cold on results, police say.

The so-called psychics on TVNZ 2 programme Sensing Murder have not produced a single piece of useful information since they took to airways over a decade ago, emails released under the Official Information Act have revealed.

The emails, including an internal police discussion about the show, and correspondence with police by a Sensing Murder researcher, showed many of New Zealand's top detective's doubted the show's effectiveness.

Sue Nicholson in action during filming of Sensing Murder.

"I wouldn't be happy to be involved with the show and don't think ... any police should.

READ MORE: Sensing Murder: in defence of the show called a 'crime against TV'

"The obvious issue is that these shows have never lead to an investigation being progressed or arrest made as far as I am aware," one detective sergeant said.

Kelvin Cruickshank tunes his psychic ability to make a reading.

Another detective inspector had reservations about police being seen to support the use of psychics as a legitimate investigative tool.

One senior investigator said while all useful information was considered, to date no information provided by psychics had resulted in the successful resolution of a case and another said Sensing Murder had never significantly contributed to any unsolved homicide.

This year's eight episode series, made by production company Screentime, featured "psychics" Sue Nicholson, Kelvin Cruickshank and Deb Webber using their extrasensory perception on three unsolved homicides and and a missing child.

Deb Webber connects with the spirits while looking into a cold case.

Police told the researcher of the show it would not become involved with one case as the homicide remained unsolved and "any commentary may well compromise any further investigation in the future".

Police also barred the use of listing police station, 0800 or Crimestoppers numbers at the end of episodes.

"I can understand your thinking on this and I'm not so fussed in sending unhelpful calls to Crimestoppers or other police lines," one officer replied to his superintendent.

Sensing reluctance from the police and their doubts of the psychic's abilities, the Sensing Murder researcher, plugged the entertainment angle of the show to boost viewer engagement.

"From my perspective, the presence of the psychics is more an entertainment angle aimed at drawing in viewers and the real strength of the programme is in the publicity that long-running investigations can get and, hopefully, new information is gleaned as a result.

"No matter what you think of the value (or otherwise) of psychics, Sensing Murder can be seen as a valuable opportunity to refresh attempts to get answers to some long-held unanswered questions, the researcher emailed.

A spokesperson from Police National Headquarters backed the comments from detectives.

"Any information we receive, regardless of its origin, is assessed to determine what, if any, relevance it may have.

"We are not aware however of any specific information arising from the Sensing Murder programme which has assisted an investigation."

TVNZ and Screentime managing director Philly de Lacey have been approached for comment.

Prior to the latest season airing in March, de Lacey was asked if she believed the psychics were credible.

"I am pretty open-minded about most things, so I don't know.

"I have no evidence of whether it is real or not real, but I have to say having produced the series, I am blown away, completely staggered by what the psychics [say], the level of details of information they've been able to give.

"One particular case where there is absolutely no way they could find any information about it - they don't know about the cases anyway when they come into production - but one case is quite historic and how they come up with dates, names and places... there's no other way you can explain it, I guess.

De Lacey said Screentime wanted people to watch the show, have discussions and debates and hoped someone may then contact police about a case.

When asked if the show was a "grief vampire" preying on family members desperate for information, de Lacey said she had made many crime shows and she found people who lost loved ones to murder had a life sentence of regret.

"You don't move on, and if there is an opportunity to talk about it and to voice your anger and upset that can be quite a cathartic experience. I've had many experiences of shows giving a sense of closure ... and if there is any chance that this series has an opportunity to help with a case, then I think that is a wonderful thing.

This year's Sensing Murder has yet to give police any leads.

POLICE PSYCHIC POLICY

"Homicide cases often attract the interest of psychics or clairvoyants. Although these individuals may genuinely wish to help, hearing their dreams and visions can cause distress to families and can give them an unrealistic sense of hope. Previous police searches for missing people actually show little or no evidence of any successful psychic involvement.

"The motive of any psychic wishing to assist should be considered, especially where they stand to gain financially for their involvement.

"Although Police will keep an open mind and assess all information which enters the investigation, care must be taken to ensure that the enquiry is not side-tracked by tabloid sensationalism that risks taking resources from other phases of the investigation.

"[Officers in Charge of] Investigations should be careful not to give credibility to claims made by psychics in the media."