The suspect, identified by his surname Lee, allegedly called at least two U.S. emergency call centers in March and April of 2012, Yonhap News Agency reported.
The Seoul Metropolitan Police Agency said that on March 26, 2012, Lee called the Warren County Communications Center in New Jersey from his home in the South Korean town of Jeonju.
Lee, 20, allegedly told an operator that he was hiding in the woods near Hackettstown High School with a gun and planned to shoot students. The call prompted the closure of eight nearby schools and a four-hour manhunt involving SWAT teams, counter-terrorism authorities and FBI officials.
Then, on April 3, 2012, Lee allegedly called the New York Police Department and said he had killed his son and planned on killing several officers and their families, too.
Seoul police officers said they caught Lee after receiving a report from the U.S. Department of Homeland Security that the calls were made from South Korea.
Police said Lee used a free smart phone application to make the calls after learning English from an American student online.