I think it is a mistake to reduce this repeated public health/safety issue to EVIL. It is not pure evil. What is evil? A classic definition is that it is the absence of what is good, from Aquinas. So, in that sense there is evil in this equation. Our public policy does not support the mentally ill, does not address the issue of domestic violence AND provides easy/legal access to firearms. This means we have created a culture that allows these shootings.
EVIL is not a force out of nowhere, a big bad devil. It is when there is a good--civic life and even perhaps the right to own guns--that is flawed. The shooters are wrong, they are criminal, they are mentally ill, they are domestic abusers, or all of the above. But the shooter is not evil, the culture that has given him access to guns is.
Don't call the shooter's acts evil. If you do, it means that there is NOTHING that can be done to prevent this symptom of evil (a lack of public policy regarding mental health/domestic violence/guns). This is not true. If the society cannot see this, they lack insight--a technical psychological term. It means you are not able to know that you are sick, as in the case of schizophrenia.
I don't know the way out of this conundrum. Except to teach my kids that access to mental health care and health care are essential, that domestic abuse is unacceptable, and that access to firearms should be regulated as part of our national security.
There is no pure evil. Pure evil is a slogan, an excuse, a smokescreen. It cripples us. It prevents insight.