A South Pasadena High School student was detained Friday after making a social media threat about gun violence on campus, police said.
The 17-year-old boy turned himself in to the South Pasadena Police Department and was taken into custody, Sgt. Spencer Louie said. The boy's identity was not released because he is a minor.
An investigation was launched Friday morning after someone had taken a snapshot of the threatening post and shown it to police, officials said.
After officers determined the post was created by a student, they went to his home, but he wasn't there, police said. They eventually managed to reach him by phone.
The threat triggered a brief lockdown of the campus, at 1401 Fremont Ave. in South Pasadena.
"There is no reason for panic," Principal Janet Anderson said in a message sent to parents. "We just want to exercise the utmost caution. All staff and students are remaining in place with doors locked."
She said staff and students were key in keeping the "situation as calm as possible."
This isn't the first threat directed at the campus.
In September 2014, two South Pasadena High students were charged with planning a mass shooting on campus.
At the time, police said the teenagers developed a plan to carry out a mass shooting and kill "as many people as possible."
The students allegedly swapped ideas over Skype about using explosives and firearms to target certain school staff members and kill classmates.
12:25 p.m.: This article was updated with a student being taken into custody.
10:20 a.m.: This article was updated with comments from Principal Janet Anderson about a suspect being located.