Investigators say an 18-year-old exchange student accused of threatening to "shoot up" his Pennsylvania high school built his own 9 mm handgun using parts he bought online and purchased 1,600 rounds of various ammunition. 

The weaponry was discovered packed inside a duffel bag belonging to An Tso Sun.

Sun was arrested last Monday after police said he threatened to carry out a shooting on May 1 at Bonner and Prendergast Catholic High School in Drexel Hill. 

Upper Darby Police Superintendent Michael Chitwood says about 663 rounds of 9 mm ammo, 425 rounds of AK-47 ammo, 295 rounds of AR-15 ammo, 225 rounds of 12-gauge ammo, and the hand-assembled gun were recovered in the bag.

Sun is a foreign exchange student from Taiwan who has been in the U.S. since August. 

He's charged with making terroristic threats.

Read more: