March 28 (UPI) -- An 18-year-old foreign exchange student from Taiwan was arrested Wednesday for threatening to "shoot up" a Pennsylvania high school, authorities said.
According to investigators, An Tso Sun, a student at Bonner Prendergast High School near Philadelphia, told a classmate not to come to school May 1 because he had planned a shooting spree that day.
An added that he was only joking, but his classmate told a teacher, who called police.
According to Upper Darby police, An's school-issued iPad showed he had searched how to buy an AK-47 or an AR-15 semi-automatic assault rifle.
Police went to the home of An's host family with a search warrant Tuesday, where they say they found a military-style ballistic vest, a high-powered crossbow with arrows, 9 mm bullets, ear protectors, a military ski mask, a loading dock for AR-15s and AK-47s and a strangling device called a garrote.
During a news conference, Upper Darby Police Superintendent Michael Chitwood said An took a high-caliber bullet to the high school -- and a classmate said he'd been shown a video of An with a flamethrower and a mask.
"When you add it all together, we believe that he was planning something horrible," Chitwood said.
The police superintendent commended the classmate who first reported the issue, and the school for how it handled the situation.
"Kudos to the person who stepped forward and helped to avert a tragedy," an Upper Darby Police tweet said.
An was booked into the Delaware County Prison Wednesday on charges of making terroristic threats. His bail was set at $100,000.