An 18-year-old foreign exchange student has been arrested for allegedly threatening to "shoot up" a Roman Catholic high school in Drexel Hill.

An Tso Sun, who is from Taiwan and has lived with a host family in Lansdowne, allegedly made the threat against Bonner and Prendergast Catholic High School, where Sun has been a student, according to the Upper Darby Police Department.

Sun allegedly warned a 17-year-old  male classmate on Monday not to come to school on May 1, saying he planned go on a shooting spree that day, police said. The classmate reported the statement to a school social worker. The school notified Upper Darby police at 9:38 a.m. Tuesday and Sun was arrested at the high school after voluntarily speaking with a detective.

Sun told police that he was kidding about the threat and had told the classmate that he was "just joking."

A search of Sun's school-issued iPad, however, showed he had searched for information on how to purchase an AK-47 or an AR-15 semiautomatic rifle, police said.

Officers executing a search warrant in Sun's bedroom Tuesday night found a military-style ballistic vest, crossbow with scope and light, 20 rounds of 9mm ammunition, military ski mask, ammunition clip loader, a strangulation apparatus known as a garrote, and other equipment, Upper Darby Police Superintendent Michael Chitwood said at a news conference Wednesday. No firearm was found.

"When you add it all together, we believe that he was planning something horrible," Chitwood said.

Upper Darby Police Superintendent Michael Chitwood unveils the items recovered in An Tso Sun’s bedroom during a press conference Wednesday morning.
6ABC / Screenshot
Upper Darby Police Superintendent Michael Chitwood unveils the items recovered in An Tso Sun’s bedroom during a press conference Wednesday morning.

Chitwood said a person would have to "be blind" to not spot the items found in the bedroom. Chitwood said Sun's host was a woman who works as a lawyer.

Enrique A. Latoison, a defense lawyer in Media retained by Sun's host, said Sun had the equipment because he was interested in a law-enforcement career and was planning to major in criminal justice at a university Latoison declined to name. He said Sun's host family viewed the items in that context.

Latoison said it was not illegal for Sun to possess any of the items found in his bedroom. Sun had brought the ballistic vest with him from Taiwan, Latoison said, and had dressed in some of the gear on Halloween at Bonner and Prendergast.

"He's not charged with any weapons offenses," Latoison added.

Sun was charged with one misdemeanor count of making terroristic threats and was being held at the Delaware County prison on $100,000 bail.

Latoison said Sun had only been in the United States for about five months and did not grasp the gravity of making such a statement — even as a joke, as Sun claimed — with school shootings currently being an extremely sensitive subject.

There is no indication that the host family, which Chitwood described as American, had a relationship with Sun before he obtained a student visa in July 2017.

Sun was set to undergo a psychiatric evaluation, Chitwood said.

Police were investigating allegations that Sun showed off a high-caliber bullet at school in February and also showed a video of him demonstrating a flamethrower while wearing a mask.

In a statement, Kenneth A. Gavin, a spokesman for the Archdiocese of Philadelphia, said: "Archdiocesan schools take the safety and security of every student, teacher, and staff member very seriously.  Thankfully, no one was harmed.  Incidents such as this demonstrate the importance of all members of the school community working together to maintain a safe environment."

He added that parents had been asked to remind their children to report any suspicious activity and had been encouraged to contact police if they had information related to the investigation.

Chitwood said the high school had no history of disciplinary issues or other problems with Sun.

A spokesperson for Taiwan's equivalent of an embassy in Washington, the Taipei Economic and Cultural Representative Office, could not be reached for comment late Wednesday.

Staff writer Robert Moran contributed to this article.