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DELAWARE COUNTY, Pa. (CBS) — A foreign exchange student who threatened to attack his Delaware County high school pleaded guilty in court on Tuesday to a federal ammunition charge.

An-Tso Sun, 18, is a Taiwanese national.

Credit: (CBS3)

He was formally charged with possessing ammunition while being in the United States on a non-immigrant visa.

Sun threatened a shooting at Monsignor Bonner-Archbishop Prendergast High School on May 1.

Authorities say they found over 1,600 rounds of ammunition and a homemade pistol in his bedroom.

Sun’s sentencing is scheduled for Dec. 11.