The man is suspected of attempted murder and a felony violation of the Flammable and Explosive Goods Act.
The police found the object in Rättvik on Wednesday. It was assessed as sharp and was rendered harmless.
"The police have an organization that works with external measures, mapping, collection and interrogation," the Swedish Prosecution Authority writes in a press release.
The prosecutor has until lunch on Sunday to request that the person be taken into custody.
