Emmanuel Costas, 18, was arrested Tuesday and charged with attempted felony murder and written threats to kill or do bodily harm, the Orlando Sentinel reported.
Police said Costas made several cryptic Facebook posts alluding to his plan to shoot up his school, such as "4/17/12 is gonna be a day to remember dat day will bring joy to me and saddness to others."
Altamonte Springs police said they were alerted to the scheme when a concerned classmate told a parent, who contacted authorities.
When police confronted Costas, he allegedly admitted posting the troublesome messages. Police said they later found documents from his backpack and home that detailed his plan to carry out a mass shooting on April 17, 2012.
Costas, who was apparently teased as a freshman, is accused of plotting to shoot fellow students at Lake Brantley High School at random during lunch.
The teen allegedly told police he respected those responsible for the 1999 shooting at Columbine High School in Colorado and he did extensive research online about the massacre in which 12 students and a teacher were killed.
The day before Costas was arrested, he posted several apologies on Facebook, saying, "I'm sorry for all the dumb threats that i said to harm people and the city of altamonte springs."
Seminole County Public Schools Executive Director Walt Griffin said the threats are "something we take very seriously."
"If the allegations are as stated, he will face expulsion," Griffin said.