Police say it is becoming clear that whoever set fire to buildings at the Whakapapa ski field on Mount Ruapehu last week had an extensive knowledge of the area.
Police say while they cannot give details, they have collected a wealth of evidence from the scene of the arson attack on 14 February in which a chalet and workshop were destroyed.
They say whoever lit the fires was determined and organised in the way they went about it.
Police say as arsonists gain satisfaction form watching their work, it its likely they would have stayed in the area for some time after the fires started.
Once the evidence is collated a profile will be built up of the offender or offenders.
Police believe there will be people who know who was behind the fires and may be shielding them.