Prosecutors said in court documents on Tuesday that two Iowa high school students killed their Spanish teacher last year because they got a bad grade.

The documents show a possible reason why the teens, Willard Miller and Jeremy Goodale, did what they did for the first time since they were caught in November 2021. The boys, who were 16 at the time, are being charged with killing their teacher, Nohema Graber, who was 66 years old.

Investigators say that Miller met with Graber on November 2, 2021, to talk about how bad his grade was in her class. Later that day, the teacher drove to a park where she walked every day after school. People saw her van leave the park with two men in the front seat less than an hour after she got there.

Investigators say that the van was left at the end of a rural road and that two boys were later picked up by a witness as they walked to town on the same road.

The next day, Graber’s body was found in the park under a tarp, a wheelbarrow, and some railroad ties. Investigators say that she had been killed with a baseball bat, and that one of the teens had bragged about it on social media.

Miller told police that he was upset with the way Graber taught and that his grade in her class was lowering his GPA.