The Spokesman-Review reported that the boys, ages 10 and 11, remained in custody on charges of conspiracy to commit first-degree murder, tampering with a witness and conspiracy to possess a firearm after they were arrested Feb. 7.
Under Washington law, children ages 8 to 12 are presumed not to have the mental capacity to form the intent to commit crime.
But Deputy Prosecutor Lech Radzimski will present court records to a judge on Feb. 20 to try to show why law enforcement officials believe they have enough evidence to overcome that presumption.
Colville police officers called to Fort Colville Elementary School began questioning the boys, who admitted the plot and gave details about how they were going to kill a girl in their class and possibly harm a half dozen other students, court documents said.
Authorities discovered the plan when a fourth-grader saw one of the boys playing with a knife aboard a school bus and told a school employee what he'd seen.
The employee asked the 11-year-old whether he had a knife. The boy "denied any knowledge of the knife" and a search of his backpack came up empty, records showed.
But a teacher suggested that the employee search the 10-year-old's backpack because he was with the 11-year-old on the bus. That search yielded a knife, a .45 caliber semi-automatic pistol and a full ammunition clip, court records showed.
A different staff member then asked the 10-year-old why he had the gun. The boy said he and the 11-year-old were going to "get" a girl identified in court documents only by initials.
"When asked what he meant by 'get' her, (the 10-year-old) responded that he and (the 11-year-old) were going to get (the girl) away from the school and do her in," court records said. The 10-year-old "further stated that the (11-year-old) was going to stab (the girl) with a knife and (the 10-year-old) was supposed to keep everyone away."
A detective who stood with the boys as they waited for transport to a juvenile hall overheard one of them tell the other: "If I find out who told them about our weapons I'm going to kill them. I don't care when I get out of jail I'm going to come back and kill them," court records said.