A mentally ill young male kills innocents. He had struggled with – fill in the blank mental illness (autism, depression, bipolar disorder, schizophrenia) – and did not receive treatment, or did not agree to treatment, or did not respond to treatment. He and his family tried to get help, but failed, and eventually his family gave up. The young man became a loner, living quietly on the margins of society, until, one day, he had enough and decided to kill himself.
Like suicide-by-cop, he decided to kill himself by killing others, thereby ensuring that police would kill him, and, if not, he could always kill himself at the end. It might be in a movie theater, or a subway station, or at a mall where a politician would speak, or – worst of all – in an innocent elementary school.
He had access to guns, yes, but it was an insane mind that pulled the triggers, a mind, often, with a treatable disease. Not infrequently, we know the disease, we know how to treat it, we have the treatments. It is sometimes the case that it is not lack of knowledge which leads to tragedy; it is the inability to implement what we know.
This is not a problem of ignorance; it's a problem of public will.