Motives aside, America needs to do something about its sick relationship with guns in general. Omar would have had a more difficult time getting his hands on an assault rifle in Germany, UK etc.
I am often amazed at how easily Americans can play around with guns and bullets. Many years ago, I visited a friend in the Mid-West who proudly showed me one heck of a private armory. (When I asked, he couldn't quite say what it was for. It seems that one can buy even assault rifles for "target practice"; but if that is the practice, what is the real target?) And in just the last month a couple of friends have posted "interesting" photos/videos on Facebook: In one, my friend was proudly showing his Glocks while at a coffee place ... "cowboy/western" style on his hips, as is permitted by the "open-carry laws" of his state (Arizona). In another, a friend in Texas showed his 9-year-old in early-morning target-practice.
At the other extreme is Japan, where even hardened criminals (Yakuza level) consider that having a gun is not worth the bother. Knife into the guts, brick to the head ..... are "OK"; but guns get the coppers really worked up, and that's not good for business. Legally getting a gun there requires all sorts of checks, including an examination by a shrink, and these have to be repeated at regular intervals. Once one has a gun and some ammo, they are subject to random police checks, and these checks include a requirement that one account for all ammo. And "misuse" is not taken lightly, which sometimes leads to bizarre cases: I recall one case in which a police officer committed suicide using his official gun. In other places, with such a tragedy, that would have been the end of it. In Japan, he was prosecuted posthumously for "improper and illegal use of a firearm". Supposedly to send a message to the public ...