Very few criminal defendants, violent or otherwise, are found not guilty by reason of insanity.

Nationally, defendants use the insanity plea less than 1 percent of the time, and more than one-third of those are murder cases. One in four of the defenses are successful.

So it’s not surprising that the Hawaii State Hospital for the mentally ill in Kaneohe may lack adequate protection against dangerous patients. But the case of Mark Davis Jr. suggests that hospital and prison officials should look for more appropriate treatment and confinement of violent mentally ill criminals.

Davis, 23, at the age of 14 raped and beat to death 6-year-old Kauilani Tadeo near her family’s Puna home in September 2001. Davis’ attorney successfully won the insanity verdict on rape and murder charges in 2005. Mental health experts diagnosed Davis as suffering mental retardation, intermittent explosive disorder and antisocial personality disorder.

After two months at the Kaneohe facility, Davis escaped. He was found two hours later in a canal nearby, was charged with escape, was acquitted by reason of insanity again and returned to the hospital.

Davis is scheduled for trial in September for an unprovoked attack with a large metal padlock on a therapist, who suffered a severe concussion from four blows to her head. Other hospital staffers were present but intervened too late to stop the blows. Once again Davis pleaded not guilty, and once again could enter the insanity plea.

Five other State Hospital patients have been prosecuted in connection with offenses at the hospital. One was convicted and returned to the hospital to serve his sentence. Another assault case is pending.

Two others were convicted of assault and are in prison, where they are not out of place. The federal Bureau of Justice Statistics reports that nearly one in five state prisoners in Hawaii are mentally ill, based on the number of inmates taking psychotropic medication — twice the national average in state and federal prisons.

Beginning about five decades ago, what has been called the national deinstitutionalizing of public mental health care has freed many thousands of mentally ill men and women who had been involuntarily committed to mental hospitals. Many of the mentally ill since then have wound up in prison, behind bars and exploited by other inmates, but not adequately aided by health care providers.

"Prisons have become the nation’s primary mental health facilities," said Jamie Fellner, director of Human Rights Watch and co-author of a 2003 study on prisons and mental illness. "But for those with serious illness, prison can be the worst place to be."

In the long run, state officials should consider centralizing and broadening the mental health care of inmates in state prisons and other secure facilities, with an arm of the State Hospital treating those convicted of violent crimes, as well as those acquitted by reason of insanity, in environments that are safer for its employees. Such an arrangement may help the hospital improve its care of patients on its present grounds without the added burden of looking after dangerous criminals in their midst.