“We don’t know for sure yet. But yes, it may have been arson,” police spokesman Björn Engström told The Local.
When no other explanation emerges in the early stages it is routine for police to begin an arson investigation.
“It’s still burning a lot. But we think the fire will be put out in the next two hours.
“When it cools down we can go in and begin investigating,” said Engström.
Part of the building had been sealed of because of the risk of collapse. But a structural expert has now deemed it safe.
While the flames in the Lindex shop have not yet been fully quelled, the rest of the Lunagallerian shopping centre was set to open again at midday.
“The shops inside the shopping centre did not have any direct fire damage but there is the possibility of smoke damage in some of them,” said Roger Magnusson from Södertörn fire brigade.
After initial uncertainty, the centre of the fire was eventually traced to the premises of the Lindex clothes shop, part of which is located underground beneath a loading bay.
Nine holes were drilled in the roof of the shop overnight, allowing firemen to spray foam down into the flames and put out most of the fires.
The fire began early on Wednesday afternoon and the shopping centre was quickly evacuated.
Soon thick smoke was seen billowing out from doors, chimneys and ventilation rooms on all six floors.
At least five people were treated for smoke-related injuries.
The smoke also meant that it was difficult to get to the source of the blaze. It took around 60 firemen from 8 stations over four hours to localise the centre of the fire.