Whanganui police have "exhausted all options" in investigating the fire which destroyed a historic Victoria Ave property in October and now say it was not suspicious.
The vacant two-storey property at 255-257 Victoria Ave went up in flames on October 29, with every available firefighter in Whanganui called in to help fight the blaze.
The building had to be demolished the next day due to safety concerns.
A spokeswoman said police had exhausted all lines of inquiry and now believed the fire was not suspicious.
"The file will be filed unless any further information comes to our attention," she said.
The building, opposite Plymouth St, was owned by the Tupoho Trust and was already slated for demolition.
The iwi bought the building in 2014 for the land, which is next to another building it owned.
The building was known for ongoing problems with squatters.
It was built in the late 1920s as a doctors' residence, with two doctors living upstairs and surgeries downstairs.