A pair of fifth-graders in a small Washington city allegedly devised a murder plot to kill their classmate, “because she was really annoying,” newly released court documents showed.

The fifth-graders, 10 and 11, had their alleged murder plot thwarted last week when a fourth-grade student at Colville Elementary School in Colville, Wash., told his teacher that he saw one of the boy’s with a knife. A teacher searched both boys’ backpacks and discovered the weapon in the 10-year-old’s backpack along with a .45 caliber semi-automatic pistol and a full clip of ammunition, the Spokane Spokesman-Review reported.

While Washington state law presumes children between 8 and 12 years old do not have the mental capacity to formulate intent to commit a crime, authorities say they have enough evidence to prove intent in this case, according to the paper.

"This was a plan. And it was a plan to kill," Stevens County prosecutor Timothy Rasmussen said, according to the Los Angeles Times. "To me, 10- and 11-year-olds do bad things. They throw rocks through windows. They shoot BB guns at people's cars. They hit people with sticks. They set a cat on fire. Those are things that children do. But this was a plot to kill."

The fifth-graders are in custody after being arrested last week and charged with murder, tampering with a witness and conspiracy to possess a firearm.

Mike Cashian, Colville school superintendent, said the fifth-graders’ murder plot came as a shock to the small Washington city.

“My background is a high school counselor and psychologist, and, quite frankly, in 30-plus years, I never heard of anything like this at this age level," he said, according to the Times.

The plot involved the 11-year-old killing the female student with the knife while the 10-year-old used the gun to prevent anyone from disrupting the murder.

“I was going to kill her with the knife and [the 10-year-old] was supposed to use the gun to keep anyone from trying to stop me or mess up our plan,” the 11-year-old said, according to court records obtained by the Spokesman-Review.

The 11-year-old told police that he used to be friends with the girl “but that he hated her now,” Colville Police Department Officer Scott Arms wrote in his report.

Arms said the boy “also indicated that [the girl] had recently become rude and would pick on him.

The 10-year-old gave similar reasons for wanting to murder the girl, telling police, “She’s rude and always made fun of me and my friends.”

The plot was so detailed that the boys were going to pay another student $80 to keep the murder plans under wraps, the Times reported.