Prosecutors demanded Tuesday a three-year sentence for a Maritime Self-Defense Force officer charged with leaking classified data on the U.S.-developed Aegis system.

Lt. Cmdr. Sumitaka Matsuuchi, 35, pleaded not guilty to violating the defense secret protection law in the first session of his Yokohama District Court trial in July.

He admitted taking the data on the Aegis air defense system for warships but denied leaking sensitive defense secrets.