NAHA (Kyodo) -- A U.S. Marine was not indicted for allegedly sexually assaulting a woman last year in Okinawa Prefecture, prosecutors said Thursday.

The serviceman in his 30s, who is in U.S. custody, was referred to prosecutors earlier this month on suspicion of committing nonconsensual intercourse that caused injury. The assault occurred in a building located in the central part of the main island of Okinawa last November.

The Naha District Public Prosecutors Office said building a case against him would be difficult based on the evidence.

Anti-base sentiment runs deep in Okinawa, which hosts the bulk of U.S. military facilities in Japan, due to aircraft noise, pollution and crimes committed by American service members.