The suspect and the girlfriend, 48, both were booked in the investigation into possible charges of abuse of a household member, Assistant Chief Henry Lau said. Additionally, he said, detectives are investigating possible kidnapping charges against the officer and an outstanding traffic warrant against the woman.

Lau said both suspects were treated for injuries apparently incurred in the argument, which generated a call to police dispatchers at 2:20 a.m. The man was treated at The Queen's Medical Center and the woman went to Pali Momi Medical Center for treatment before both were booked, he added.

Police arrived at the ground-floor apartment in the Hibiscus Hill townhome complex, 94-1459 Waipi‘o Uka St. Soon after police arrived, Lau said, the woman walked out of the apartment and one of the officers heard the sound of a weapon being "racked," or prepared for loading.

Police then took the woman to a secure location nearby, Lau said, and Specialized Services Division officers, including a crisis negotiation team, were summoned. These forces arrived at about 4:30 a.m.

Investigators are still trying to determine why the male suspect failed to answer phone calls to the apartment or respond to officers addressing him through a bullhorn, Lau said, although officers suspect he may have been sleeping and may have unplugged the phone.

He added that a search warrant is being sought to determine whether a firearm, which never was seen by officers, was used in the incident.

At about 8:20 a.m., Lau said, the standoff ended when the suspect walked out the front door, partially dressed in his police uniform and apparently preparing to go to work. He seemed unaware that armed officers had assembled outside the home, he said.

"I understand he was very surprised when he walked out the door," Lau said.

The apartment is in the Q building of the complex and is about four rows in from the street. The other residents of the building of eight apartments were evacuated, and officers barricaded access to interior buildings during the standoff.

Lau said that the officer is being held in the police cellblock; if detectives release him pending the conclusion of the investigation, he would return to duty but will be assigned to a job away from public contact.

The officer, with the police force for 10 years, currently is assigned to the Wahiawa district, Lau said.