Investigators have found traces of gunpowder in the wreckage of a sunken South Korean naval ship, a government official said on Thursday, further bolstering suspicions of a North Korean attack. Along with four pieces of aluminum collected from the scene earlier, the gunpowder adds to a possible evidence of a torpedo attack. Aluminum is a key element used in making torpedoes, and officials said the aluminum found appears to be different from the ship's structure. The finding reinforced suspicions that the Cheonan patrol ship came under an attack from North Korea before breaking in half and sinking near the two Koreas' tense Yellow Sea demarcation line on March 26, killing 46 crew members, the Yonhap news agency reported.