It was yet another grim discovery: The bodies of three unidentified men suspected to be from North Korea were found Tuesday, washed ashore on a beach in Fukaura, Aomori Prefecture, just over a week after a small wooden boat was found in the area.

The latest find has further deepened a mystery that has captured the attention of the Japanese public in recent weeks — an apparent surge in the number of wooden boats from North Korea that have been found on and just off the Sea of Japan coast.

Over the past two months, local authorities have already uncovered debris from five similar boats in the same town, with all believed to have come from Japan's isolated neighbor.