At a press conference, police described how the fire was started from the outside, using plenty of kindling and other flammables. They believe the people they have in custody can be linked with the alleged arson.
"We have detained more than one person. They are Finns but I won’t say anything more at this point," said Bengt Renlund, Porvoo's Police Chief Commissioner.
Police are still urging people who might have seen something Sunday night to call a hotline at 019-548-6461.
"We’ve received more tips yesterday afternoon and evening. And we still need more of them so we can compare that information with what we have already gathered."
The fire destroyed the roof of the cathedral, causing the massive chandeliers to crash, but most of the interior and its treasures were spared. It will nonetheless take years to restore the church, which is one of Finland’s most cherished historical landmarks.
The fire was able get such a swift grip on the roof because the smoke detectors only worked on the inside. A passing cab driver reported the smoke to emergency services minutes before the alarms went off.
In the end, the entire roof was destroyed but miraculously, or rather through the delicate work of the fire fighters, the ceiling and supporting beams held fast, protecting much of the interior and its treasures.
Fire fighters also worked hard to keep the flames from leaping over to nearby wooden buildings in Porvoo's historic old quarter.
In the end, porvoo's Bishop Erik Vikström is saddened but optimistic. He believes the cathedral will be rebuilt swiftly.
The 600-year-old cathedral was supposed to be the centrepiece of Porvoo’s bicentennial celebrations in three years’ time. It is also a focus of summer tourism and weddings.
The oldest parts of the building date from the 15th century, and it has suffered two other devastating fires in its long history. It was almost completely destroyed and rebuilt in the 1700’s.