Cazenovia, Wis. ? A teenager who pried open his family’s gun cabinet brought two weapons to his rural school Friday and shot the principal to death after a struggle with adults and other students, authorities said.

The 15-year-old, identified as Eric Hainstock, was taken into custody and charged as an adult with murder, the district attorney said. No one else was hurt.

Authorities said Hainstock had complained about being teased by other students and decided to confront teachers and the principal using a shotgun and handgun taken from his parents’ bedroom. The shooting also came one day after the principal gave him a disciplinary warning for having tobacco, according to a criminal complaint.

Witnesses said Hainstock walked in with the shotgun before classes began. A custodian, teachers and students wrestled with him, but he broke through, took out the handgun and shot Weston Schools Principal John Klang three times, Sheriff Randy Stammen said.

Dave Thompson, the custodian, said Hainstock was a special-education student who told him he was there to kill someone, but did not say who.

“He was calm, but he was on a mission,” said Thompson, 43, who also has two children at the school.

Klang, 49, was shot in the head, chest and leg, authorities said. He died hours later at a hospital in Madison.