Police said the suspect had anonymously befriended a group of fellow students a week before the threats against them began. A female student then reported the threats to police, who traced them to the teen.
According to students, it has been a tense couple of days since they heard of the threats being made online.
"I was kind of scared," said Millikan student Sara Bermudez. "I was like, 'wow these kinds of things are happening at school.' You come to learn."
"Many times people think that by posting information online, once it is removed it can't be traced," said Sgt. Rico Fernandez from Long Beach police. "That's not correct. Any threat or any communication that's made online in cyberspace can be traced."
Carmelita Spalding said her daughter was afraid to come to school because of the threats.
"I just told her that she needed to go to school because we didn't want a truancy," said Spalding. "She got really scared and said she didn't want to be shot at. And she started crying, so I said, 'okay Katie you can stay home, we'll just deal with it.'"
The suspect was arrested Thursday morning. A computer and other devices were confiscated from the teen's home.
The boy has been charged with making criminal threats and obstruction of justice. He was booked at the Long Beach Police Department's Youth Services Division and later released to his parents.
The juvenile division of the Los Angeles County District Attorney's Office is conducting its own investigation to see what criminal charges could be filed against the teen.