Investigators suspect that another lieutenant commander in the Maritime Self-Defense Force was involved in the leak of classified data on the Aegis combat system that was revealed earlier this year, police and MSDF sources said.
The sensitive data and documents were found in January at a home of a crewman who did not have proper security clearance. A separate lieutenant commander was initially suspected of giving him the information.
The documents, which were recorded on a hard disk, were found during an investigation into the Chinese wife of the crewman, who is a petty officer 2nd class. The Chinese woman was suspected of violating the immigration law.
The material included data subject to the Japanese-U.S. mutual defense assistance agreement, and was produced around 2000 by an MSDF unit in Yokosuka, Kanagawa Prefecture. The unit develops and services computer systems for Aegis ships, reconnaissance aircraft and other equipment.
The material was designed for use in training MSDF cadets learning to handle the Aegis vessels' advanced air defense systems.
The lieutenant commander in question belonged to the computer system unit for about 1 1/2 years between 2001 and 2003 and made trips to the United States to study the Aegis system, the sources said.
The material was later found at the MSDF First Service School in Etajima, Hiroshima Prefecture, where it was copied by instructors and passed on to students. It was eventually passed on to the crewman.
The Kanagawa Prefectural Police and the MSDF's police unit are expected to expand the investigation and search the home of the officer and other relevant places on suspicion the secrecy protection law was violated the sources said.