The Seoul Metropolitan Police Agency said Monday in a statement that a 19-year-old surnamed Lee made calls from South Korea to a New Jersey communications center and threatened to use an AK-47 to kill students at Hackettstown High School.
The calls led schools in the northwestern New Jersey town and at Centenary College to keep students inside for four hours while police searched the area.
South Korean police began investigating after U.S. authorities traced the calls to South Korea. Police say Lee used a smartphone application to make the calls.
Police declined to provide contact information for Lee. The statement says he's serving in the military.