The boys broke into the St. Ambrose Catholic School at 363 SE 12 Avenue on June 23, said investigators.
"That decision really messed me up in so many things right now," said 14-year-old Nicholas Knisely (pictured, above).
WATCH: Surveillance video
Video surveillance shows Knisely -- the shirtless one wearing pink pajamas -- and his two friends walking around the school two days before breaking in, police said.
The teenagers discharged several fire extinguishers throughout the classrooms and on the property, police said. They vandalized vending machines and threw paint on the furniture, computers, and walls.
Knisely said boredom drove them to do it, and admitted to using a hammer to destroy a vending machine and several windows.
"If I could take it back, I really would. When we went in there, we really didn't plan to destroy anything really. It just happened," he said. "It was mostly me who did most of the things, and I'd like to say that before my two friends get in trouble for most of the work that I've done."
The teenagers also broke several cabinets and made themselves a meal, leaving their DNA on used utensils for detectives to gather as evidence, said investigators.
All three were charged with burglary structure, felony criminal mischief, grand theft of fire extinguisher, and molesting coin operated machine/larceny. The other two boys were 15 and 14 years old.
"I'm sorry to the church, to the priest. I'm sorry to my friends. I'm sorry that I brought my friends into this and it really wasn't their fault," said Knisely.