ALPINE, Calif. (FOX 5/KUSI) -- An elementary school in Alpine was placed on lockdown Wednesday morning after the discovery of ammunition onsite, according to school officials and the San Diego County Sheriff's Office. SDSO received a call around 9:51 a.m. after a student at Shadow Hills Elementary found a bullet in a fifth-grade classroom and told his teacher, who then turned it into the school office. Potential death threats at Alpine elementary school concern parents The school, along with Creekside Early Learning Center and Mountain View Learning Academy, were all placed on lockdown to ensure the safety of students and staff, the Alpine Union School District said in a statement to families. All backpacks were searched during the lockdown. According to the district, after a thorough investigation, officials determined the bullet was brought to school by a student who explained they found it during a recent camping trip and decided to keep it to show to their family. However, it later fell out of the student's pocket at school. "This type of behavior is not acceptable and will have serious consequences to ensure the safety and well-being of our entire school community," the district stated. "We greatly appreciate the cooperation of the Alpine Sheriff's Department, students, staff and parents during this time. As always, the safety and well-being of our school community are our highest priority." Federal agencies address concerns about reported drone sightings The lockdown was lifted at 11:30 a.m. Deputies determined there was no active threat and nothing was found on campus. The incident comes on the heels of a 'kill list' found at Shadow Hills Elementary last month that was reportedly written by two 10-year-old girls. The list included the names of 14 students and two staff members, prompting parents to speak out at the school district's Board of Trustees meeting on Monday.