A South Carolina teen has been sentenced to 10 years in prison and says he's sorry for scaring people with a plot to blow up his high school.

Nineteen-year-old Ryan Schallenberger did not give a reason Thursday for why he made the written and recorded plans that referred to committing "Columbine II."

The plans were uncovered last April when his parents intercepted a package of ammonium nitrate, which can be an ingredient in homemade explosives.

U.S. District Judge R. Bryan Harwell said the teen needed to go to prison because his actions were serious, but gave him credit for his clean record.

The judge also noted Schallenberger was diagnosed with depression and obsessive-compulsive disorder. The teen's attorneys have attributed the plans to his mental illness.