BARABOO, Wis. — According to prosecutors, when Eric Hainstock entered his high school in September 2006 armed with a rifle and a handgun, he shouted, "I'm here to kill someone."

Hainstock made good on his vow, fatally shooting John Klang, 49, the school's principal, during a scuffle over one of the guns.

Hainstock is charged with first-degree intentional homicide in Klang's death. During opening statements Friday, prosecutors portrayed Hainstock's behavior as deliberate. The defense, while not disputing that Hainstock killed Klang, countered that Hainstock's actions were reckless, but not intentional.

For Hainstock, 16, the jury's determination of whether Hainstock's acts were deliberate or spontaneous will have profound consequences. Hainstock could face life in prison if he is convicted of intentional homicide. Reckless homicide, on the other hand, carries a 40-year maximum sentence.

In opening statements on Friday, Sauk County District Attorney Patricia Barrett sought to portray Klang's death as the almost-inevitable outcome of a series of events on Sept. 29, 2006. In her view, Hainstock acted logically, methodically, and intentionally. (VIDEO)

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The path to Klang's death began Sept. 14, when Klang suspended Hainstock for three days for throwing a stapler at a teacher. High school librarian Kay Lamborn testified Friday that Hainstock seemed "proud" when the stapler incident was published as a police blotter item in the local paper. Hainstock asked Lamborn if she could make a copy of the story for his father, but she declined.

County Sheriff's Deputy Joel Vodak also testified about the incident, painting a somewhat different picture of Hainstock's attitude. Vodak, who was dispatched to drive Hainstock home from school, said Hainstock was worried about his punishment.

"He said he was punished by being made to run around the yard," Vodak said.