You do not know that the shooter wasnt schizophrenia. That is a disease that comes on suddenly in the early 20s. He may not have been diagnosed, but well never know.
If his brain is autopsied they will. The cells in the brain message centers of schizophrenics are disordered. In normal brains, they go the same direction in a line. At least, when I did a lot of research on the disease years ago, that was the case. I can't imagine it's changed. Whichever mental illness or disorder this young man had was definitely NOT under control. I do hope a national discussion on mental illness will result from this incident, but I'm not holding my breath.