(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. 
 
 Three California students injured after gun on police motorcycle discharges 
 
 Teacher slayings hurt view of schools as safe havens 
 
 CNN's Greg Morrison, Drew Iden and Tina Burnside contributed to this report. ||||| A A 
 
 An 11-year-old boy was arrested on suspicion of attempted murder Wednesday night after Vancouver police officers found a handgun and more than 400 rounds of ammunition at Frontier Middle School, 7600 N.E. 166th Ave. 
 
 The school and adjacent Pioneer Elementary School were put into lockdown Wednesday about 9:20 a.m. for two hours. 
 
 Officers said they also found several knives, according to a press release distributed about 10 p.m. Wednesday. 
 
 There were no injuries in the incident. 
 
 The boy is a student and was booked into the Clark County Juvenile Detention Center. 
 
 The Vancouver Police Department Major Crimes Team is investigating. 
 
 Police spokeswoman Kim Kapp said investigators with the department’s Major Crimes Unit started conducting interviews around 11:30 a.m. that continued well into Wednesday night. 
 
 The Facebook page for Evergreen Public Schools was flooded with comments from parents, most concerned that they weren’t notified of the lockdown. 
 
 “As a parent, any incident that involves my children even in the vicinity of a weapon constitutes an emergency and I have the right to be informed,” said Tara Nolan Monroe in a comment thread on the district’s Facebook page. “Any parent who is involved in and concerned about their children would not want to learn of a situation like this after the fact, particularly from a public institution.” 
 
 Others acknowledged that they primarily want their children to be safe, even it means being left in the dark about what’s happening on campus. 
 
 Parents were primarily alerted about the incident through the Frontier and district Facebook pages, along with the district website, said Kris Fay, spokesman for Evergreen Public Schools. Some parents heard about it through local news outlets or text messages from their children. 
 
 While middle school students were sent home with a letter outlining the incident, elementary school students did not get a letter because they were on an early release schedule, Fay said. 
 
 “I really hope Evergreen uses this as a huge learning experience and changes the way they notify parents in an emergency such as this. Yes, I want all resources directed at keeping my children safe but if someone can take the time to post on Facebook, they should be able to initiate the flash alert system,” said Brenda Lehto Hudson on the Facebook page. 
 
 A small group of parents at each school in the Evergreen district subscribe to the FlashAlert system, Fay said, which sends out email and text message notifications. However, the third-party system is unpredictable and often delayed in sending out emergency information, Fay said. Fay said that the district has found the quickest mediums to reach parents are Facebook and the school website. The district would consider integrating FlashAlert into its emergency alert system if more parents used it. 
 
 An estimated 900 students attend Frontier Middle School and about 600 attend Pioneer Elementary School. 
 
 NOTE: Due to several insensitive and even offensive remarks, we have disabled the comments on this story.
– A pretty jarring story out of Washington state, where an 11-year-old boy was last night arrested and faces an attempted murder charge following the police discovery of a handgun, more than 400 rounds of ammunition, and several knives at a Vancouver, Wash., middle school. No one was hurt in the incident, which prompted a two-hour lockdown at the middle school and an elementary school next door yesterday morning, the Columbian reports. The boy has been placed in juvenile detention, CNN reports.