i don't know. it's a good question. on the flip side, do you really think that someone who is disturbed enough to want to kill a whole bunch of people they have never met before in their life is going to be able to hide it?
from Holmes' wikipedia page:
"Holmes' defense attorneys claimed in a
motion he was a "psychiatric patient" of the medical director of Anschutz's Student Mental Health Services prior to the Aurora shooting; however, the prosecution disagrees with that claim.
[42][43] Four days after the release of the defense attorney's motion, the judge required this information to be blacked out.
[44] CBS News later reported that Holmes met with at least three mental health professionals at the
University of Colorado prior to the massacre.
[45]
Some of Holmes' acquaintances suspected prior to the shooting that Holmes suffered from mental illness and could be dangerous. Two weeks before the shooting, he sent a text message asking a graduate student if they had heard of the disorder
dysphoric mania, and warning the student to stay away from him "because I am bad news."
[46]"
so, yeah, at least for him it seemed like it was at least somewhat well known/suspected that he had struggles with mental illness.
and, again, no system is going to be perfect, of course people are going to slip through the cracks, but that seems like a bad reason to say we should do nothing, doesn't it? doesn't it sound wrong to you to say "oh, well this won't work 100 percent and some people may or may not be able to beat the tests, so it's best if we just do nothing at all?"