An-Tso "Edward" Sun, 18, was arrested last March after another student reported that he told him he planned to open fire in the school in Upper Darby, on the edge of the northeastern city of Philadelphia.

"Hey, don't come to school on May 1st ... I'm going to come here armed and shoot up the school. Just kidding," Sun told the other student, according to prosecutors.

When police searched the room that Sun had been occupying with his host family, they found a semi-automatic pistol and 20 rounds of ammunition, as well a crossbow, arrows, and a bullet-proof vest, helmet and pants.

The mother of the host family told police that she had earlier removed from the student's room more than 1,600 rounds of ammunition -- including magazines for AK-47 and AR-15 assault-style rifles -- and a homemade pistol, which the police took custody of.

On November 19, he was sentenced to time already served in prison and ordered to be deported from the United States and permanently banned from returning.

Sun was handed over to Taiwanse officials "without incident," immigration officials said.

The United States experiences an average of one school shooting per week, according to a CNN count.

In February, a 19-year-old man killed 17 people in a school shooting spree in Parkland, Florida, while in May, a 17-year-old student, using a gun belonging to his father, killed 10 people in his high school in Santa Fe, Texas.