Mr Hansen was last seen on November 24, 2013. His disappearance began as a missing-person investigation and was upgraded to a homicide inquiry in early December.
The bodies of Mr Hansen and his dog Henry have yet to be found.
Detective Senior Sergeant Simon Harrison, in charge of the investigation, said police had worked tirelessly on the case.
Two Whanganui Police officers had been involved in the investigation for the past two months.
"There is still much work to be done, with the main focus of returning Mr Hansen to his family," Mr Harrison said.
Police still want to speak to anyone with information about the whereabouts of Mr Hansen and his dog. Anyone who can help is asked to contact Detective Dave Wilson on 06 213 9595 and information can also be provided anonymously to Crimestoppers on 0800 555 111.