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The head of the Kayo Matsuzawa murder inquiry says he may have to make some "hard decisions" on the future of the case before Christmas.

Detective Senior Sergeant Kevin Baker said it was possible police might never learn how the Japanese tourist died and who placed her naked body in a fire alarm cupboard in a downtown building in Auckland.

The case has proved extremely difficult for police because of a lack of forensic evidence and a pathologist's inability to find the cause of death.

The body was discovered in a locked cupboard off a stairwell in the Centrecourt building in Queen St on September 22 - 10 days after Miss Matsuzawa was last seen alive.

Detective Senior Sergeant Baker said he would decide in the next week or two whether to scale the inquiry down considerably.