A strange tale of a disaster averted comes to us from Pennsylvania this week, but it’s one which may generate more questions than answers. An Tso Sun is an 18-year-old foreign exchange student from Taiwan who came to Pennsylvania last summer. He was preparing to attend a Catholic high school in Upper Darby, a suburb to the west of Philadelphia. But something went wrong over the course of the exchange student’s stay here and now he’s in jail after authorities were alerted to some of his strange behavior and social media postings. What they found in his room added up to a kid about to engage in a mass shooting at this school… maybe. (CBS Philadelphia)

An Tso Sun, an 18-year-old student from Taiwan, moved to the U.S. last August to attend Bonner and Prendergast Catholic High School in Drexel Hill. Police say he told a friend that he was planning to shoot up the school. He’s now been charged with making a terroristic threat. “One of my teachers saw him getting walked out in handcuffs,” said senior Brian Dunphy. Dunphy shared math class with Sun during first period, but he said it was Halloween when he noticed his behavior. “He wore, like, a full military costume. It looked pretty legit,” said Brian. “He did have a fascination with guns. People overheard him talking about guns. I guess the right person told and that’s why they took action.”

As the authorities repeatedly tell us, if you see something, say something. And in this case, somebody did. Sun reportedly had brought a bullet (not a gun) to school and was showing it around. His collection of camouflage clothing and gear was enough to alarm his fellow students. He’d been looking up information about AK-47s on his school iPad. He posted a video of himself wearing a mask and wielding a flamethrower. Most alarmingly, he called one of his friends and told him not to show up to school on May 1st because he was going to shoot the place up. That’s clearly enough of a group of “signs” that the cops had to take action, right? If they had ignored those types of signals and the kid had actually shot up the school it would have been a total failure on their part.

But when they took Sun into custody and searched his room, here’s what they found, as listed in the report: “a military-style ballistic vest, ski mask, military web gear with pouches to hold ammunition clips, a high-powered crossbow and arrows, a bullet loading dock for an AR-15 and AK-47, an empty box for a gun-making kit, 20 live round, ear protectors for firing, and a strangulation device called a garrote.”

Notice one thing missing from that list? They didn’t find an actual gun. There was a box for a gun-making kit. A modest amount of ammunition was found. (Let’s be honest… twenty rounds isn’t all that much.) And he had a crossbow, but when you consider how long it takes to reload a crossbow compared to the firing rate of any decent semiautomatic firearm, it’s not quite as much of a threat. The garrote is certainly worrisome as a visual, but it’s also not an implement for mass murder unless all your victims are sleeping.

So what happens when this guy (who is now 18) goes to trial? He never actually did anything violent. And they don’t even have a firearms charge on him unless a gun turns up later. Do they just have to let him walk? Or perhaps cancel whatever type of visa exchange students use and send him back to Taiwan?

That brings me to the other question Sun raises. We’ve learned more than enough about illegal aliens, people who overstay tourist visas and all the rest. How many high school foreign exchange students come to the United States each year? I did some checking and the number is pretty high, in the tens of thousands. (When you include college and university students it’s over a million.) Presumably, the ones going to high school here all have to qualify for an F-1 visa. ICE has a program set up to track them while in the United States known as SEVIS (the Student and Exchange Visitor Information System). Both schools and sponsoring families are supposed to enter and regularly update information in SEVIS about the exchange students.

But how are they vetted before they’re accepted to the program? Assuming Sun was perfectly normal back home and he just went off his rocker after moving here, that might not have caught him. But what if he had a juvenile criminal record? Would we know that when he applied to be an exchange student?

There aren’t too many answers along those lines on the ICE website that I was able to find. But it’s a question worth looking into. This is one subset of the immigrant population which may not be getting as much scrutiny as required because we’re just assuming that kids won’t be as much trouble.