(CNN) -- A Washington state middle school boy was arrested after he brought 400 rounds of ammunition, multiple knives and a handgun to his school, intending to shoot another student who he thought was bullying his friend, police said.
The 11-year-old was booked into a juvenile detention facility Wednesday after the incident that caused the lockdown of Frontier Middle School, Vancouver Police said.
No one was injured.
Authorities were alerted by the boy's mother, who called the school concerned that her son may have taken kitchen knives with him that day, according to a probable cause document. The boy was patted down by school resource officers who found the weapons and ammunition.
The boy told school officials that "a voice in his head was telling him to kill" an 11-year-old classmate for calling the boy's friend gay, according to the probable cause document.
"He stated a voice told him killing (the classmate) was a good idea; however he planned to just shoot (the classmate) in the arm and then shoot himself in the head," the document said.
The boy is being held on charges of attempted assault, unlawful possession of a firearm and possession of a weapon at school.
He earlier faced a charge of attempted murder, but prosecutors did not immediately find sufficient evidence to support the charge. However, Kasey Vu with the Clark County Prosecuting Attorney's Office left open the possibility that the attempted murder charge could return when prosecutors receive more information from the investigation.
The school in Vancouver was locked down for about two hours. Students were sent home with letters alerting parents of the situation, said Kris Fay, a spokeswoman for Evergreen Public Schools.
The incident comes on the heels of several school-related violent incidents around the nation.
On Monday, a math teacher was killed and two students wounded by a boy who then killed himself in a Nevada school. On Wednesday, a math teacher was found dead in the woods northeast of Boston; her 14-year-old student is accused of killing her.
CNN's Greg Morrison, Drew Iden and Tina Burnside contributed to this report.