A 13-year-old boy intentionally killed his English teacher because he was angry over a failing grade and being suspended for throwing water balloons, a prosecutor said Wednesday.

Nathaniel Brazill faces life in prison without parole if convicted of first-degree murder in the killing of teacher Barry Grunow at Lake Worth Middle School on May 26, 2000, the last day of classes.

Brazill was angry because a school counselor had suspended him and sent him home earlier in the day, Assistant State Attorney Marc Shiner told jurors.

But the defense in its opening statements repeated what it has maintained for months, that Brazill pointed the gun at the teacher only to force him to let him talk to two girls in the classroom. Then the gun went off accidentally, said defense attorney Lance Richard.

"As he's holding the gun up to Mr. Grunow, he's overwhelmed with tears," Richard told the jurors. "His hand begins to shake and the gun discharges. The gun discharged in the hands of an inexperienced 13-year-old with a junk gun."

But Shiner told jurors Brazill was receiving a final "F" grade in Grunow's class and also was angry he wasn't being allowed to talk to the girls. Grunow "had no idea of the rage, hate, the anger, the frustration" filling the seventh-grader, the prosecutor said.

Grunow, 35, was shot in the head with a .25-caliber semiautomatic pistol stolen from Brazill's grandfather's house days earlier.

"He pulled the trigger. He pulled the slide back," Shiner said of Brazill. "He made the conscious decision to kill."

Police have reported that Brazill told a classmate he was going to return to school and shoot the counselor who suspended him. He told the girl he'd be "all over the news."

The shooting in an outside hallway was captured on a school surveillance camera.

Shiner told the jurors that Brazill had a fascination with firearms and knew how to use the gun. But Richard said his client, whom he described as a nonviolent prankster, was interested in guns because he wanted to pursue a career in law enforcement.

Brazill, now 14, could be found guilty of lesser charges such as second-degree murder or manslaughter of the jury decides he did not form the intent to kill Grunow, a father of two and basketball coach.

The trial is expected to last about two weeks.