CHESTERFIELD, S.C. -- The South Carolina teen who was accused of plotting to blow up his high school has pleaded not guilty to three federal explosives charges.

Ryan Schallenberger, 18, was arrested in April after his parents picked up a package addressed to him containing 20 pounds of ammonium nitrate. Police found other items in their home, leading them to believe the teen planned to set off bombs at Chesterfield High School.

If convicted on all charges, Schallenberger would face a maximum of 40 years in prison.