HOUSTON -- A northwest Harris County middle school student was arrested Friday after bringing a handgun to school, officials told KPRC Local 2.

Authorities said the unidentified 12-year-old female student at Dean Middle School, located at 14104 Reo St., threatened to kill a teacher and students, and was sent to the office at about 8:30 a.m. for starting a fight. She was then suspended, and her parents picked her up.

Deputies said they wanted to charge her, but the district attorney declined.

"At that point, they refused the charges on the basis that there was no imminent threat at that time," said Chief Larry Shiflet with the Harris County Precinct 4 Constable's Office.

Officials said the girl returned to school three hours later with a loaded gun, and wearing a bandana and hat.

She entered the gymnasium and pointed the gun at three teachers and a maintenance worker, deputies said.

"She just pulls out the gun. Everybody -- they just started screaming, 'Lock down, lock down, lock down,'" a student said.

Harris County Precinct 4 deputies then intervened at gunpoint.

"For everyone's safety, we wanted to make sure no one was injured," Shiflet said.

The girl was immediately isolated from students, according to authorities.

The campus was placed on lockdown during the incident. Students were detained in classrooms for about 15 minutes until officers took the student into custody.

The principal sent home a letter to parents explaining what happened.

Officials said no students were in danger at any time.

The student faces two counts of assault with a deadly weapon. She could possibly be charged as an adult.

Investigators are trying to determine where the student got the weapon.