"They were arrested during the night. Several quite quickly after the crime was committed, and several later," Thomas Agnevik, police spokesman in Östergötland, told news agency TT.
Police received the alarm at 11:30pm on Monday that a man had been shot at Nygårdsskolan in Skäggetorp, just outside of Linköping. When police arrived at the scene one man had already been shot dead and another had suffered gun wounds.
The injured man, 29, was first taken to the hospital but has since been transferred to police for interrogation. Sixteen additional men were arrested on suspicion of murder and attempted murder.
"We recognize several of the names from the so-called gang crimes earlier," Agnevik said.
Police found empty shells at the scene but refused to confirm if they had found a gun. The man who was shot dead has not yet been identified.
Officers hinted that the fatal shooting was likely gang related.