A South Carolina teenager arrested for plotting to b**** his school had designs for an arsenal of explosives including a nail b**** that would have "devastated" students in a crowded hallway, a local police chief said today.

Ryan Schallenberger, 18, called his plot "Columbine III" and laid out details in a "b**** summary" that described the different types of explosives he would use in the suicide attack. He even recorded his expenses.

"I think he was more concerned about a high body count than killing anyone in particular," Chesterfield Police Chief Randall Lear told ABC News.

Schallenberger's "summary" contained details for a nail b****.

"Inside a school, with confined concrete walls, just a little bit of nails, nuts and bolts, ball bearings and some of these explosives devices, it would devastate the student body," Lear said.

Authorities arrested Schallenberger on Saturday after a package arrived at his family's rural South Carolina home and his parents opened it to find 10 pounds of ammonium nitrate, a substance that can be used as an explosive when c****ined with diesel fuel or another accelerant.