The juvenile court initially found probable cause only for an attempted assault charge and two other counts, but the Clark County Prosecutor's Office later upgraded the charge to first-degree attempted murder, the court documents show.
A juvenile court administrator also ruled Tuesday that the boy should remain in custody. He cursed the administrator after her ruling and then swore at security officers who escorted him out of the courtroom after he refused to leave, the Columbian reported.
The boy, who is not being identified by KOMO News, claimed in the presence of Frontier Middle School officials that a "voice in his head" was telling him to kill another 11-year-old student at the school "for calling his friend ... 'gay.'"
The boy was arrested last week after police said he was found with a gun, seven knives, 478 rounds of .22-caliber ammunition and a pair of two-way radios at Frontier Middle School, court documents show. No one was hurt, and the school is now back to normal.
The boy's mother called the school and said her son had taken some kitchen knives, and another student at the school told a school resource officer that the boy was armed.
The school resource officer took him to the principal's office where police said they found a .22-caliber handgun in his pants pocket and two loaded magazines in another pocket. More ammunition and the knives were found in the backpack.
Court documents released Tuesday show the boy faces five other criminal charges beyond the attempted murder charge - theft of a firearm, unlawful possession of a firearm, and three counts of possessing dangerous weapons at a school facility.
The newly released documents say the boy originally planned to cut and shoot his victim on Monday or Tuesday of last week as buses were loading after school, so that it would be witnessed by a large number of people.
But he didn't follow through on those days because he was having trouble figuring out how to shoot the gun. On Wednesday, however, he had figured out how to disengage the safety, court documents say.
He then decided to shoot his victim during first-period band class, but then changed his mind again and intended to carry out the shooting later.
Police said in the affidavit the boy told authorities he planned to shoot the student he felt was bullying his friend "in the arm and then shoot himself in the head."
He was interviewed and arrested before he could carry out his plan.
A mental health evaluation of the boy has been completed, and Juvenile Court Commissioner Jennifer Snider denied his release after reviewing the evaluation. Snider says his family had ignored the advice of mental health professionals and the boy has anger management problems that intensify when authority figures give him instructions.
His competency will be reviewed again at a Nov. 12 hearing.