Two 15-year-olds have confessed to setting fire to a school building in Espoo last week, police announced on Monday.
The two teens were detained on Sunday as suspects in the blaze, which broke out at the Laurinlahti school on Friday evening.
The fire destroyed most of the school building's roof.
The blaze was one of a number of fires around the city in recent months. Police suspect that a number of groups of children in elementary and middle schools were behind the recent fires.
According to the case's lead investigator, Klaus Geiger, the two 15-year-old suspects were not former pupils of the school. The facility was not in use at the time of the blaze, as pupils have been attending school at other premises since the autumn.
Geiger said on Sunday that the preliminary investigation's criminal classification would be specified later.
"It is either a question of arson or aggravated arson. As the investigation moves forward, it will become clear whether the individuals are suspected of other arson cases, as well," Geiger explained.
Geiger has previously suggested there were unconfirmed suspicions that the fires may be linked to so-called social media challenges.
"There are several kinds of challenges on social media where the kids copy each other," he said, adding that the police have received about one hundred tips about the fires. However, Geiger did not specify which social media platforms may have been involved.
But police have emphasised that a connection to social media is merely suspected.
"We received several tips via social media. Citizens have also come forward with tips," he explained.
Geiger noted that the city has seen several suspected cases of arson since the beginning of the year. The incidents started with small fires in rubbish bins and skips.