Investigators probing the sinking of the Navy corvette Cheonan has apparently discovered a smoking gun pieces of a propeller of a torpedo, which is believed to have sunk the ship - which means North Korea. They compared the collected pieces of a North Korean torpedo test was taken in the West Sea seven years ago, and also analyzed traces of gunpowder found in the wreckage of Cheonan, an official said. The government is to present the findings Thursday.