Three Roosevelt High School freshmen were charged with making a terroristic threat Tuesday after the school was placed on lockdown, North East Independent School District spokeswoman Aubrey Chancellor said. The freshmen included two 15-year-old girls and a 14-year-old boy, Chancellor said. Authorities discovered two plastic guns during the lockdown and there was no active shooter, Chancellor said. The school had received a threat on Monday. This is the third incident this month involving a weapon at an NEISD campus. "Around 9:30 a.m., a student reported that another student was seen with a gun walking down the hallway. We immediately went into our lockdown procedures and contacted (district police)," a letter sent to parents by principal Bryan Norwood reads. "Three students have been identified and taken into custody. It was determined that the student did not have an actual gun, but instead, fake toy guns. " Lights were turned off throughout the school and students were instructed to lay on the ground while police searched the campus. Chancellor said that is the protocol whenever a weapon is found on campus. Dozens of panicked parents arrived to the school after news spread about the potential threat. MORE NEWS ON KSAT.COM: Student found with loaded gun at San Antonio middle school With multiple layers of security in place, NEISD focuses on student safety As school year looms, NEISD confident in security measures On Monday, Principal Bryan Norwood sent a letter to parents about a previous threat administrators were notified about. Officials were "made aware of a phone call to a student that threatens violence on campus." "While police do not believe this is a credible threat, we want to be transparent, and we must take every threat seriously," Norwood wrote in the letter. It isn't clear what exactly prompted the lockdown or the discovery of the plastic guns on Tuesday or whether the Monday threat was related. KSAT received multiple calls from concerned parents about the incident. Fake Guns on Campus Roosevelt High School letter sent to parents