Detective Inspector Craig Scott told Fairfax suspected homicides were treated the same as all other missing persons cases.
"The files of missing people are never closed. However, further investigations are initiated when new information comes to hand, regardless if the file is thought to involve foul play or not," he said.
"These files remain open until the missing person, or their body or remains, are located."
Scott Watson remains in jail convicted of one of New Zealand's most controversial murders after 17-year-old Olivia Hope and her boyfriend 21-year-old Ben Smart boarded a yacht in the Marlborough Sounds with a man in the early hours of New Year's Day 1998 and were never seen again.
Watson was convicted of killing the pair despite their bodies never being found.
He has steadfastly maintained he had no involvement in their disappearance.
Kirsa Jensen went missing in 1983 while riding her horse.
She was last seen beside an old gun emplacement near the mouth of the Tutaekuri River in Hawke's Bay. Her horse was found tethered nearby. Police believe Kirsa was abducted and murdered.
Another high-profile cold case is that of Mona Blades, who disappeared on May 31, 1975.
She was 18 and was last seen hitching a ride in a orange Datsun in Taupo.
There were other sightings of the car but no more of Mona. The driver was nondescript: middle-aged, bald, fat and possibly wearing glasses.
