An unnamed man in his 20s was arrested Thursday following a large explosion at Hässleholm technical school, initially investigated as a possible terrorist attack.

Investigators have since downgraded the explosion, which they believe to have been directed to cause general devastation to the area but did not harm anyone, and have said that the suspect in custody acted alone, SVT reports.

The exact cause of the explosion, whether or not it was made by a bomb and the details of the explosive, has not been released so far by police, nor have they given details about the identity of the suspect or any potential motives.

Local police area manager Pär Cederholm explained why the investigation had initially been regarded as possible terrorism saying they factored in that it took place in a public area and that it had potentially been purposely targeting bystanders.

“We rate this event as a single isolated event. We also judge that it is not a terrorist offence,” Cederholm said, and added that there was damage at the scene from the explosion but did not specify to what extent.

‘Attack Against Our Democracy’: Bombing of Swedish Police Station ‘May Be Terror’

https://t.co/YJDTC4JESZ — Breitbart London (@BreitbartLondon) October 18, 2017

Local pupil Filip Öberg, 18, who attends the school, said the explosion was so strong it shook the ground around him. Other pupils claimed the suspect wore a mask which was not confirmed by police who simply said he wore clothing which made it clear he did not belong in the school.

While Sweden has only suffered one major fatal terror attack in recent years, the 2017 Stockholm massacre committed by Islamic radical and failed asylum seeker Rakhmat Akilov, the country has seen a number of criminal explosions and bombings.

The most notable bombing occurred last year in Helsingborg when the front of a local police station was almost entirely destroyed in what then-prime minister Stefan Löfven called an attack on democracy.