Los Angeles police arrested a middle school student allegedly in possession of a “ghost gun” and planning a school shooting.

The Los Angeles Sheriff’s Department announced the arrest Friday after receiving reports of a 13-year-old student, whose name was withheld because of his age, planning an attack on Ánimo Mae Jemison Charter Middle School. Several students overheard the  alleged threat and told teachers, who notified school administrators. The sheriff's office opened an investigation Thursday. 

After tracking down the alleged student, police obtained a search warrant and conducted a search of the student’s home Friday. Officers said they found an AR-15 “ghost gun,” along with plans and gear to carry out the alleged threat.

Giffords Law Center to Prevent Gun Violence notes “ghost guns, which include firearms assembled from kits or made with 3D printers, are untraceable by law enforcement and often undetectable by metal detectors.”

Undersheriff Tim Murakami posted an update of the situation on Twitter shortly after the arrest Friday morning.

The threat comes one week after a shooting at Saugus High School in Santa Clarita, California, by a student armed with a “ghost gun.” He reportedly bought multiple parts online and assembled the weapon before using it to shoot five students, two of whom died. The shooter died from a self-inflected gunshot the next day.

The student from the charter school is in custody and facing potential charges of making criminal threats. Police also took a relative of the accused student into custody. 

Massachusetts police Representational image of a police officer using his K9 to check a car near John Joseph Moakley United States Courthouse in Boston, Massachusetts, on April 6, 2015. Photo: Scott Eisen/Getty Images