Captain Patrick Yoes said the boy is in a juvenile facility under a $100,000 bond. Investigators said they tracked down the boy through a computer IP address that pointed to his home.
"His comments were he was curious to see what the reaction would be," said Yoes.
The teen told authorities he'd met Pine Forest High School students in an online chat room, and he looked up more information on them via Twitter. That's how he was able to post real names, and make the threat appear real.
"I think the message here is sometimes people feel some kind of anonymity behind a keyboard and computer screen, but it is very easy for us to track you," said Yoes.
The threat was first posted on Edmodo, an intra-school system website, and then shared by others on other sites like Instagram, Facebook, and Twitter.
The posting read like a heartbroken, bullied boy who had enough -- stating he would shoot up Pine Forest High School before killing himself.
The threat prompted extra law enforcement on campus, the cancellation of Saturday's Homecoming dance, and an open investigation by the Sheriff's Department and Cumberland County schools.
School officials said only 663 student were in class Monday at Pine Forest. Nearly 1,000 students did not come to school, meaning 60 percent of students stayed home.