The unidentified defendant faces charges of first-degree attempted murder, use of explosives and possession of explosives, and two counts of felony menacing, prosecutors said.
He will be tried as an adult, and evidence showed he had a "long-term interest in explosive devices" and may have had a larger plan for violence, they said.
A teacher found the explosive device -- which police described as similar to a pipe bomb -- inside Centaurus High School in Lafayette May 13, forcing the school's evacuation, The Denver Post reported Friday.
2014: The Year in Fashion [PHOTOS]
Cyclist struck and dragged underneath car