An 18-year-old Taiwanese exchange student accused of threatening to shoot up his Delaware County Catholic high school built his own 9 mm handgun using parts he bought online and purchased 1,600 rounds of ammunition for a variety of firearms, investigators said Monday.
The weaponry was discovered packed inside a duffel bag belonging to An Tso Sun.
Sun was arrested last Monday after police said he threatened to carry out a shooting on May 1 at Bonner and Prendergast Catholic High School in Drexel Hill. He's charged with making terroristic threats, a misdemeanor.
"When we add it all up, there is no doubt in our minds that he was planning something," Upper Darby Police Superintendent Michael Chitwood said during a news conference on Monday.
About 663 rounds of 9 mm ammo, 425 rounds of AK-47 ammo, 295 rounds of AR-15 ammo, 225 rounds of 12-gauge ammo, and the hand-assembled gun were recovered in the bag, Chitwood said.
Sun's host mother in Lansdowne, Pennsylvania removed the armaments from the teen's bedroom after the school contacted her about the alleged threat, Chitwood said. Authorities are questioning why she removed the bag and mulling whether she'll face charges.
The ammo and gun parts were bought over the internet since Sun arrived to the United States in August, Chitwood said. He went online on a school-issued iPad at least 20 times to search about guns or to buy ammo and gun parts.
That internet research included visits to websites about AR-15 and AK-47 assault-style rifles — which have been used in a string of mass shootings — and Chitwood believes it shows Sun was attempting to purchase the weapons.
During a search of Sun's bedroom on Tuesday, police recovered other items including a military-style ballistic vest, military-style web gear with pouches to hold ammo clips, a crossbow with scope and seven arrows, a loading dock for rifle clips, 9-mm ammunition and a strangling device, police said.
During the course of the investigation, Chitwood said police found the duffel bag.
Sun, who is in the U.S. on a student visa, legally obtained all of the weaponry, Chitwood said.
Sun's family and and a former tutor said the teen long had an interest in weapons and protecting others from harm. He also once built a flamethrower.
His now former attorney, Enrique Latoison, previously said the teen never intended to carry out a shooting. He said Sun lacked "the same social skills of what it is to grow up in the post-Columbine generation" in not understanding the magnitude of his comment to a classmate.
Latoison has since withdrawn from the case. NBC10 has reached out to Sun's new attorney, Robert Keller, for comment on the new developments.
Additional charges have not been filed in the case. Sun remains in the Delaware County Jail on $100,000 bail ahead of a preliminary hearing next week.
Chitwood said Homeland Security would be reviewing the case this week. Detectives are still working to determine whether any other people may be involved with the threat.