The Crown says phone calls between the defendant and a man who leased a storage unit in Wellington which was torched earlier this year, establish the motive of the fire.
A 35-year-old man who has been granted name suppression denies a charge of arson.
The fire caused extensive damage to 390 units at the Kiwi Self-Storage facility in Kilbirnie in April, including the loss of Oscar statutes and historical documents.
Practically everything in Block B of the facility was destroyed either by fire or water damage.
Hundreds of customers lost their possessions and millions of dollars of damage was done.
Opening the crown's case, prosecutor Sally Carter told Justice Simon France the crown's case is based on various layers of circumstantial evidence.
But the defendant's lawyer, Douglas Ewen, said the case was one where the identity was the issue.
Ms Carter said CCTV footage from the facility showed a person entering the gate of the Kiwi Self-Storage premises, with a significant amount of clothing on to bulk out their appearance.
The Crown said the person was wearing a yellow and white vodka cruiser cap, holding a plastic bag and a red fuel tank, but their face was not visible. The cap was part of a liquor store promotion.
Ms Carter said the accused had the pin code to unit 1001 of the facility, which was rented by a friend, and that unit was one of three which has been accessed shortly before the fire started.
But under cross examination from the defendant's lawyer, Douglas Ewen, the Wellington manager for Kiwi self storage, Gregory Lane, admitted that if someone was in the facility for more than an hour and did not leave the premises the system resets.
"That would mean if someone was there before 11.30 the system would reset and it wouldn't show them being on the property, would it," Mr Ewen asked.
"It would reset the unit about an hour later," Mr Lane told the court, adding that if a person was still in their unit then the alarm would go off.
Mr Carter told the court just prior to the fire the friend received a text from the defendant's girlfriend saying: "Could you please answer your phone ... he really needs you right now, you are the only one that he needs now, please."
The man did not respond and the Crown said it was a falling out between the two which precipitated the fire.
Phone calls between the pair and intercepted by the police, will be played in court and go to the motive, she said.
The Crown said the accused was seen on CCTV footage walking towards the unit and then a short while later walking back from the unit wearing different clothing, now wearing a dark black purple cap.
A black cap with a purple peak was found on the site of the units and the defendant's DNA was found on it, she said.
The accused denied owning the cap, but was seen on CCTV footage on the days before the fire, wearing an identical cap.
She told the court the Crown alleges that the person who lit the fire using the petrol in the tank discarded it in the fire with the outer layer of the clothing.
A witness will also tell the court, he bought a fuel tank for the accused, similar to that seen on the CCTV footage, before the fire.
The defendant denies having a fuel tank.
The man who bought the tank also bought a fuel line assembly and a brass connector, which was found in the defendant's car.
The facility is a secure gated premises with entry gained by an pin code key pad. A customer's pin is individual to the unit, which opens the main gate and then deactivates the alarm on a customer's unit.
Customers exit by a separate gate and are again required to enter their pin which reactivates the alarm on their unit.
Ms Carter said there were several attempts to use the friend's code to leave the building, which were not successful and it was believed the person must have gone over the gate or the fence.
CCTV at the exit gate was not working.
The court heard rebuilding what was lost will take three years and cost $3 million, plus the $750,000 in income that the company has lost.
The judge-alone trial is expected to take two weeks.