Police are sending victims of crime letters telling them their cases will not be investigated because they are not considered high priority.

The practice has been highlighted in the case of a South Auckland dairy owner who supplied police with video footage of a man stealing from his shop.

He was told by letter six days later that no attempt would be made to catch the thief.

The letter, signed by Papakura Sergeant Shane Fogarty, said a high volume of complaints and limited resources meant each complaint was evaluated in terms of the likelihood of offenders being caught and prosecuted.

It said the seriousness of the offending was also taken into account.

"Obviously the higher rated files get precedent [sic]. Those that are at the lower end of the scale regretfully have to be filed," the letter read.

"Your complaint falls into the latter and I am left with no alternative other than to record and file this matter."

Police Minister George Hawkins and Police Commissioner Rob Robinson refused to comment on the case yesterday without knowing the specifics.

Police public affairs general manager Michael Player said: "Obviously we don't keep cases forever where we've taken the action we can reasonably take in the circumstances."

Such letters were part of police policy to reply to all complaints.

"It sometimes means that not every single complaint goes a lot further but they're all taken seriously."

Mr Player said the practice varied from district to district on whether some complaints were filed rather than investigated. Inspector Dave Montgomery, area commander for the southern part of Counties Manukau district, said such letters were regularly sent in his area, depending on workload.

"There's always more crime than we have the capability to deal with and it's just a matter at what level we are unable to pursue a complaint.

"If there is a high volume of complaint you have to prioritise at a higher level than other times when the workload is light."

He said the letters were not symptomatic of a lack of resources.

"There will be times when we can't cope no matter what your resourcing is. That's the nature of crime, it's something we can't predict."

He refused to comment on the dairy owner's case but planned to examine the file today to see if police had taken the appropriate action.