The janitor at Castle Rock Middle School discovered six bales of hay, doused with what appeared to be gas and oil, stacked against the back entrance of the school Thursday morning.
Gas cans were scattered around the hay bales on the receiving dock.
"Our first concern was the safety of our students and staff," said Principal Shaun Harrington.
Harrington immediately notified the police and fire departments, which arrived at the school and investigated the scene. Agents from the Department of Alcohol, Tobacco and Firearms were also brought in.
Harrington said agents swept the school before classes started to make sure inside the building was safe. Nothing was found.
The school's loading and receiving area is currently roped off with crime scene tape as police investigate.
Harrington praised the Castle Rock's school resource officer, Kelly Compton, who was Harrington's first point of contact.
"We went right to Kelly," Harrington said, and he took it from there.