When we looked at the thwarted school shooting in a suburb of Philadelphia last week there were plenty of unanswered questions. 18-year-old An Tso Sun, a foreign exchange student from Taiwan, had given warnings that he was going to shoot up Prendergast Catholic High School in Drexel Hill. When law enforcement searched his room he was found to have all manner of alarming, military-style equipment and apparel, including a crossbow and some ammunition, but they initially didn’t report finding an actual gun.

Now that their investigation is closer to completion, it turns out that there actually was at least one weapon, but Sun didn’t acquire it in the typical fashion you might have expected. He allegedly built it himself from parts he ordered online. (CBS Philadelphia)

Upper Darby police say a foreign exchange student who was arrested last week for threatening to shoot up his school had built a gun with over 1,600 rounds of ammunition.

Police say 18-year-old An Tso Sun of Taiwan, a foreign exchange student at Monsignor Bonner Archbishop Prendergast Catholic High School, had hundreds of rounds for an AR-15 and AK-47 and a 9 mm handgun he built himself from parts purchased online. The parts are virtually untraceable. He was allegedly planning to unleash carnage on the school May 1.

According to Upper Darby Police Superintendent Michael Chitwood, Sun had approximately 225 rounds of 12-gauge ammo, 663 rounds of 9 mm ammunition, 295 rounds of AR-15 ammunition, and 425 rounds of AK-47 ammo, along with other sorts of ammunition.

Each new detail being released makes this story more and more disturbing. Authorities initially reported finding only twenty rounds of unspecified ammunition and no gun. It turns out that the veritable mountain of ammo and the gun were in a bag in Sun’s room, but after law enforcement contacted Sun’s host family about the allegations, somebody moved the bag, apparently in an attempt to hide it. The host parent is being questioned about this now.

The second issue to address is the fact that this kid (who was 17 when all of this began but has since turned 18) was somehow able to purchase all of the parts online needed to build his own handgun. Now, the majority of the replaceable parts on a handgun can be ordered online from outlets such as Brownells or Midway. The available parts might surprise people not involved in gunsmithing as a hobby, and they include magazines, grips and even triggers. But there’s one critical part you aren’t supposed to be able to purchase directly and that’s the receiver (frame) of the weapon. Without that, you basically have a pile of parts but no ability to fire a shot.

You can order a receiver from those outlets legally, but unless you happen to be the holder of an FFL (Federal Firearms License) you can’t legally have the frame shipped directly to you. You can still order one, but the distributor would need to ship it to your local FFL holding shop where you would go to pick it up after successfully completing your NICS background check.

So, knowing all of this, how did this seventeen-year-old kid get his hands on a 9 mm handgun frame? Did he acquire it from a dishonest or incompetent dealer or was he able to find one on the black market? That’s one of the many questions DHS (who have been called in on the case now) will be seeking to answer moving forward. ICE has a detainer on Sun and he’s no doubt subject to deportation at some point, but they’re going to need to get to the bottom of this near calamity first. Sun’s family has arrived in the country from Taiwan and he’s being represented by a law firm.