Mentally disturbed 23-year-old Mark Davis Jr., acquitted in the shocking rape and murder of a 6-year-old girl nearly a decade ago, could once again raise the insanity defense for a new assault charge.

If he does and prevails, he will be returned to the Hawaii State Hospital, where he is accused in the assault case of repeatedly slamming a padlock on the head of a hospital therapist.

Davis would be raising the insanity defense for the third time, also having been acquitted of escape from the state hospital just two months after he was committed to the Kaneohe facility.

The case highlights the quandary law enforcement and hospital officials face when dealing with troublesome patients acquitted of crimes because of their mental condition. Those patients must remain under the hospital’s supervision until a state judge determines they are no longer mentally ill or no longer dangerous.

Some, especially those acquitted by reason of insanity in murder cases, remain at the state hospital for decades or the rest of their lives.

Because of their mental condition, those patients usually raise the insanity defense to charges of committing crimes while at hospital.

If convicted of the second-degree assault charge, Davis could spend up to five years in prison.

Upon his release, however, he would be sent back to the hospital, according to lawyers and hospital officials.

In one of the state’s most horrific crimes, Davis was 14 and a Hawaii island resident when Kauilani Tadeo was raped and beaten near her family’s Puna home on Sept. 27, 2001. She died from a blow to her head.

Prosecutors said Davis admitted that the police investigation proved he sexually assaulted and killed the girl. But mental health experts had diagnosed Davis as suffering from mental problems that included mild to moderate mental retardation, intermittent explosive disorder and antisocial personality disorder.

In 2005 he was acquitted of the murder and rape charges by reason of insanity and committed to the state hospital.

Two months after he was committed to the Kaneohe facility, Davis escaped for a couple of hours before he was found in a canal near a shopping center at Temple Valley. Davis was charged with escape but was acquitted by reason of insanity and returned to the hospital.

IN THE PAST FIVE years, five patients other than Davis have been prosecuted in connection with offenses at the hospital, according to hospital administrator Mark Fridovich.

One was convicted of escape and sentenced to prison and returned to the hospital after he served his sentence.

Another patient has an escape charge pending.

Two patients were convicted of assault and are now in prison. Another patient has a pending assault case.

City Deputy Prosecutor Mark Yuen said the office is prosecuting Davis because the determination of whether he is legally insane will be made later, based on mental examinations.

"We are just holding everyone penally accountable for whatever action they did," he said.

Davis pleaded not guilty to the assault charge. His trial is scheduled for September.

In that case, Davis is accused of an unprovoked attack on an occupational therapist on May 20, 2009.

The hospital staff was trying to place restraints on him after he told a social worker he was going to kill someone or escape, according to a police report.

But Davis walked or ran to a room where the therapist was at a table with another patient in an assessment session, the report said.

Davis grabbed a 13⁄4-inch combination padlock the therapist was using in the assessment, hit the therapist four times on the head with the metal lock and said several times, "I’ll kill her," the document said.

The therapist said she suffered a severe concussion, the report said.

Police began an investigation but didn’t submit the final closing report until May, clearing the way for prosecutors to file the assault charge on June 28.

During the investigation, James Ornellas, the hospital’s clinical safety coordinator, checked on the case with police several times and asked that charges be pursued so Davis could be transferred to the Oahu Community Correctional Center, according to the police report.

Davis’ arrest report lists him as 5 feet 9 inches tall and weighing 300 pounds.

Davis has been transferred to the OCCC while his case is pending.

Deputy Public Defender Bryant Zane said it’s too early to say whether he will raise the defense for his client, but said it definitely will be considered.

Despite Davis’ past, there is no guarantee that he will be acquitted by reason of insanity.

Under state law the defense must show that defendants suffer from mental disorders that render them incapable of distinguishing right from wrong or abiding by the law. The mentally ill can still be convicted if they have those capacities.

One notable example is is Byran Uyesugi, who was diagnosed with schizophrenia but was convicted of murdering seven Xerox co-workers in 1999, despite his insanity defense.