The recent fatal shooting at Northern Arizona University has left some asking not only why a student would attack his classmates, but also why a weapon was on hand in the first place.

Arizona’s public universities are gun-free zones, unless the weapon is stored securely in a car and out of sight. The suspected shooter, who police say killed one student and injured three others at NAU, was keeping his firearm in a car.

But there's no way to tally how many weapons are actually being stored in this way at Arizona universities. NAU, Arizona State University and the University of Arizona do not require a person to report if they have a gun in a vehicle on campus.

According to public records, however, illegal possession of weapons cases are fairly rare at these three universities. A review of recent crime statistics shows, altogether, there have been about 20 weapons law violations between 2012 and 2014 — 13 of those at ASU’s Tempe campus.

ASU would not comment specifically on those violations or the circumstances surrounding them.

Sgt. Filbert Barrera with the UA police department said most violations they see are not because a student is found carrying a weapon.

“It’s not very frequent that we actually respond to somewhere on campus, like say the residence hall," Barrera said, "and we go there and contact someone with a gun and arrest them because they are doing something wrong."

Barrera said much of their patrol work is also geared toward keeping the campus safe from outsiders.

“I would say the majority of them [the violations] are contacts we make during traffic stops," Barrera said.

The disclosure of campus safety statistics, which is required under a federal statute known as the Clery Act, apply to any violation committed by a person on campus or adjacent public property involving a weapon.