Police searched a sunken tour boat off Japan's northernmost main island of Hokkaido with a drone Tuesday but found no signs of 12 people who remain missing, officials involved in the search operation said. The authorities had struggled to search the inside of the 19-ton boat that sank more than a week ago with 26 people aboard and was found on Friday at a depth of 120 meters off the Shiretoko Peninsula. While previous attempts to search the ship with the camera-equipped device failed due to strong swells and currents, the Hokkaido police managed to send the drone into the submerged vessel a few times on Tuesday, according to Japan Coast Guard officials taking part in the operation.