Prosecutors, not police, decide formal charges under Japan's criminal justice system. (Matthew M. Burke/Stars and Stripes)

CAMP FOSTER, Okinawa — Japanese police arrested a U.S. Navy sailor early Sunday who allegedly entered an apartment unit on Okinawa while under the influence of alcohol.

Seaman Apprentice Nathan Walker, 20, assigned to Helicopter Sea Combat Squadron 25 at Andersen Air Force Base, Guam, was still in police custody Monday in Okinawa city, an Okinawa police spokesman told Stars and Stripes by phone that day.

He was detained at 5:05 a.m. Sunday in the hallway outside the apartment in the Miyagi district of Chatan town, the spokesman said.

Police were not sure how Walker entered the home, the spokesman said. The door was undamaged and no one was injured during the incident, he said.

A breath test measured Walker’s blood alcohol content at 0.15%. For comparison, all 50 U.S. states have set 0.08 as the legal limit for driving under the influence or driving while impaired.

A neighbor called police at 4:43 a.m. to report a “foreign man” was attempting to open the apartment’s front door, the spokesman said.

Walker denied the allegation, the spokesman said.

The Navy acknowledged Walker's arrest in an emailed statement Monday and said the incident is under investigation.

"The Navy takes all allegations of misconduct seriously, and we continue to monitor this case closely," wrote Lt. Cmdr. Andrew DeGarmo, a spokesman for Task Force 76.

Police planned to send his case to prosecutors on Monday to consider filing charges, the spokesman said.

Some government officials in Japan speak to the media on condition of anonymity as a requirement of their employment.