That's not a bad thing, really. And I'm sure the Hitchcock movie will be wonderful and a bit more meaty than usual Hollywood fare.
The causes: a preliminary and shallow summation would include schizophrenia, bipolar disorder, family violence. Evil---only under the now emerging definition as the "absence of empathy" which I find more accurate and sympathetic. I feel for the gunman, who committed suicide. Obviously, his suffering was tremendous and could not, for whatever reasons, couldn't get help. The real story is, Why did he kill his mother?
Eighteen children died: shouldn't we be relieved that those children don't grow up into bodies which will experience pain and maybe manifest mental disorders not unlike what our gunman suffered?