Approximately 1.1% of the US adult population is schizophrenic. Approximately 2.6% of the adult US population has bipolar disorder—over four fifths considered severe.
The shooter in Arizona, most are presuming at this time, carries at least one of these diagnoses.
These are treatable illnesses, often first presenting in the early twenties (in the case of schizophrenia)—with a rub. The longer the mental illness goes untreated—the more years one lives in a psychotic state—the less and less effective the therapies become. This medical fact is known as the kindling effect. A mind left burning out of control in paranoid delusions becomes ever harder to reground in reality.
Much has been made of the lack of gun control in Arizona—the ease by which a mentally disturbed man could acquire deadly weapons. Let's not miss the other half of the coin here: Arizona is also a terrible place to be mentally ill—becoming ever more difficult to get treatment as the Tea People have their way, and gut the few remaining social services and treatment options available to those with little to no resources.
And, let's not forget that our own community—Washington State, King County and Seattle all—are cutting mental health services. Just by statistics, we can expect about 75,000 people in Washington State to be schizophrenic. As we cut these services, the kindling effect will make recovery later next to impossible.