Many if not most killers are not thought or known to be "crazy"--or engaged in criminal behavior--before they blow their tops. That is why we often hear what we are hearing now about this guy--completely shock and surprise that he would do this. As I've said, millions of people have mental issues of one kind or another that can simmer at low level for years --and whatever the issue may be goes undiagnosed and untreated. There are tons of people walking around with anger issues, low-to-moderate depression; people who might drink too much; people who are pissed about one thing or another or life in general. We are talking about a huge pool of people--and so even if a tiny fraction of them ultimately flip their lids and go out and easily buy guns and ammo...well, this is why we have a ton of mass shootings in America.
Conservatives and Republicans always want to frame these mass shootings as completely abnormal--just a rare crazy person: nothing can be done; it's not the guns. That's nonsense. This is COMMON in America and has been common for 20 years or longer. Everybody wrings their hands and "says prayers" and is shocked, and then nothing changes and everyone carries on until the next mass shooting in a couple of weeks. It goes to show how stupid America is nowadays--unwilling to tackle real problems. This is a serious problem with conservatives and Republicans--oh, we don't want to inconvenience the gun industry, or saddle polluters with regulations; they never want to do anything. For conservatives, nothing is really a problem, because that would mean regulation and perhaps constricting earnings a few companies for a time--and we can't have that. Better to have people dying of gun violence and health problems, right?