Porirua Police are treating the fire that destroyed the Porirua timber framing factory, Brooker & Hall Ltd, on Raiha Street on Tuesday 1 May as suspicious.
Detective Sergeant Shane Rongonui says police are treating the fire as suspicious because at this stage there is no obvious natural cause.
An ESR scene examination and forensic tests may yet provide further information.
As part of their investigation, Police are talking to other businesses in the area and people who travel through the area.
"We would like to speak to anyone who has information that might assist with the investigation of this fire.
"We are interested to hear from anyone who was in the area between midnight on Monday and early Tuesday morning. They may have been driving on or near Raiha Street in Elsdon and seen something unusual or someone acting suspiciously. We want to know about anything that was a bit out of the ordinary for that time of the morning."
Detective Sergeant Rongonui says it's possible the fire could have been going for some time before emergency services were called around 5.30am on Tuesday, so any suspicious sightings in the general area could be relevant to the investigation.
He also says it's highly likely that if someone has been involved in lighting the fire, the people close to them will have noticed suspicious behaviour, such as someone taking an unusual interest in the fire, appearing to know a lot about it, or just saying something unusual in passing.
Anyone with information can contact either Detective Sergeant Shane Rongonui or Detective Constable Terry Laws at Porirua Police on Tel: 04 238 1400.
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For more information contact Detective Sergeant Shane Rongonui
Tel: 238 1400.