Updated

Nearly a year after a 16-year-old shot and killed his principal, jurors will be asked to decide if he was a bullied, immature child or a murderer bent on revenge.

Eric Hainstock is charged with first-degree murder and is being tried as an adult in the shooting death of Weston Schools Principal John Klang. If convicted, he could face life in prison. Hainstock's trial was to begin Thursday.

According to a criminal complaint, Hainstock told detectives he took guns to Weston the morning of Sept. 29 because he was upset that Klang and other school officials had done nothing to stop fellow students from teasing him. He told investigators he wanted to make people listen to him.

But Klang rushed him in a school hallway and tackled him. Hainstock told detectives he shot the principal three times during the struggle. A wounded Klang managed to take the gun from Hainstock.

Sauk County District Attorney Pat Barrett has portrayed Hainstock as a selfish liar who reacts violently whenever adults tell him what to do. He is expected to introduce evidence at the trial that in the two weeks leading up to the shooting, Hainstock threw a stapler at a teacher and a book at a student, saying "I am going to laugh when everyone in this school gets hurt."

Hainstock's attorneys, public defenders Rhoda Ricciardi and Jon Helland, have said Hainstock was bullied and that teachers looked the other way.