Police arrested a 15-year-old student after he allegedly brought an AR-15 and ammunition to a Phoenix high school on Friday, authorities said.
The student is facing "serious felony charges" after allegedly bringing the semi-automatic rifle — the weapon behind a dozen of the 21 deadliest mass shootings in the U.S. since 2006 — to Bostrom High School, where he was arrested in the main office around 1 p.m. on Friday, according to a news release from the Phoenix Police Department.
Authorities also allegedly found more ammunition in the student's backpack and lunch box, according to the police department.
School officials alerted police after "others on campus" told them "that the student may have a gun," Donna Rossi, director of communications for the Phoenix police, told NBC News.
Administrators received the alert about the possible weapon on campus during the lunch time at the school, a spokesperson for the Phoenix Union High School District said in a statement.
The spokesperson added that “school personnel reported a possible weapon on campus based on an initial, anonymous tip” but did not elaborate further.
The school went into a lockdown "as soon as school officials were notified of the possible gun on campus," Rossi added. A spokesperson for the school district said the lockdown lasted a little over one hour.
School officials looking into the allegation of the possible weapon "discovered the report was accurate and local authorities intervened and confiscated the weapon," the statement from the school district said.
The student was booked into juvenile detention on charges including "minor in possession of a firearm, carrying a weapon on school grounds, interfering with an educational institution and other weapon related charges," Rossi added.
The student remains in custody, and the police department's crime gun intelligence unit is investigating alongside school and district officials, according to the news release from Phoenix police, who have not publicly identified the student.
"We commend those who originally reported the possibility of a weapon on school grounds to adults on campus who immediately called police," a statement from the police department said.
It was not immediately clear how the student obtained the gun and ammunition or what his intent was in bringing them to school. The police department did not respond to those questions, and the school district spokesperson did not know the answers to them.
The spokesperson added that the federal Family Educational Rights and Privacy Act prevents them from being able to release the student's disciplinary records.
The statement from the school district said officials "are grateful to those who reported this incident to trusted adults."
"As always, the safety and well-being of our staff, students, and visitors remains our top priority, and we will work with law enforcement as they continue to investigate," the statement added.
In a letter sent to families Sunday, school officials said there would be additional safety measures in place Monday "out of an abundance of caution," and that no backpacks would be allowed on campus this week. Officials will also host a meeting with parents in the school cafeteria on Monday night, the letter states.
"We recognize the severity of this situation and the fear and anxiety it causes our students and staff," the letter said, adding that there would be "social-emotional support available at school" for students and staff.
Rossi and police Sgt. Robert Scherer directed further questions about the student's bail status, when he is next due in court and the potential sentence he could face if convicted to the Maricopa County Attorney's Office and the Juvenile Department of the Maricopa County Superior Court.
An official with the Maricopa County Attorney's Office said the office "does not comment on juvenile cases." The police spokesperson said the investigation is ongoing.
The school district describes Bostrom High School as an “alternative center” that provides a “small school environment that focuses on student-centered learning while simultaneously supporting the whole student.”
Arizona does not ban semi-automatic rifles, but prohibits minors from buying or possessing a gun without written consent from a parent or guardian, according to the Giffords Law Center to Prevent Gun Violence, a nonprofit gun control advocacy group. The state also bans firearms on school grounds, except by those authorized to carry them or for use in approved school programs, according to the Giffords Law Center.
The Phoenix incident comes just days after an 18-year-old shooter in New Mexico used three weapons — including an AR-15 — to fatally shoot three elderly women: Shirley Voita, 79, Melody Ivie, 73 and her mother Gwendolyn Schofield, 97. The shooter was killed by police on Monday following his deadly rampage.
As mass shootings have increased, calls have intensified to place restrictions around sales of semi-automatic rifles like the AR-15, which was originally created for military use and is now copied by a variety of manufacturers under different names.
With their ability to fire bullets at a fast speed, AR-15s are known to inflict extensive damage to the human body and are more likely to be deadly than other firearms are.
Washington state banned semi-automatic rifles last month, becoming the ninth state with such a ban, plus Washington, D.C., according to the Associated Press. President Joe Biden has called for a national semi-automatic weapons ban in light of the increase in mass killings.