SEOUL, South Korea — The way U.S. officials see it, there's little mystery behind the most notorious shipwreck in recent Korean history.
Secretary of State Hillary Rodham Clinton calls the evidence "overwhelming" that the Cheonan, a South Korean warship that sank in March, was hit by a North Korean torpedo. Vice President Joe Biden has cited the South Korean-led panel investigating the sinking as a model of transparency.
But challenges to the official version of events are coming from an unlikely place — within South Korea itself.
Armed with dossiers of their own scientific studies and bolstered by conspiracy theories, critics dispute the findings announced May 20 by South Korean President Lee Myung Bak, which pointed a finger at Pyongyang.
They also question why Lee made the announcement nearly two months after the ship's sinking, on the very day campaigning opened for fiercely contested local elections. Many accuse the conservative leader of using the deaths of 46 sailors to stir up anticommunist sentiment and sway the vote.
Pyongyang denies involvement in the sinking and calls the accusation a fabrication.
The critics, mostly but not all from the opposition, say it is unlikely that the impoverished North Korean regime could have pulled off a perfectly executed hit against a superior military power, sneaking a submarine into the area and slipping away without detection. They also wonder whether the evidence of a torpedo attack was misinterpreted, or even fabricated.
"I couldn't find the slightest sign of an explosion," said Shin Sang Chul, a former shipbuilding executive-turned-investigative journalist. "The sailors drowned to death. Their bodies were clean. We didn't even find dead fish in the sea."
Shin, who was appointed to the joint investigative panel by the opposition Democratic Party, inspected the damaged ship with other experts April 30. He was removed from the panel shortly afterward, he says, because he had voiced a contrary opinion: that the Cheonan hit ground in shallow water and then damaged its hull trying to get off a reef.
"It was the equivalent of a simple traffic accident at sea," Shin said.
The Defense Ministry said in a statement that Shin was removed because of "limited expertise, a lack of objectivity and scientific logic," and that he was "intentionally creating public mistrust" in the investigation.
The doubts about the Cheonan have embarrassed the United States, which is beginning joint military exercises today in a show of unity against North Korean aggression. On Friday, an angry North Korea warned that "there will be a physical response" to the maneuvers.
Two South Korean-born U.S. academics have joined the chorus of skepticism, holding a news conference this month in Tokyo to voice their suspicions about the "smoking gun" — a piece of torpedo propeller with a handwritten mark in blue ink reading "No. 1" in Korean.
"You could put that mark on an iPhone and claim it was manufactured in North Korea," scoffed one of the academics, Seunghun Lee, a professor of physics at the University of Virginia.
Lee called the discovery of the propeller fragment five days before the government's news conference suspicious. The salvaged part had more corrosion than would have been expected after just 50 days in the water, yet the blue writing was surprisingly clear, he said.
"The government is lying when they said this was found underwater. I think this is something that was pulled out of a warehouse of old materials to show to the press," Lee said.
South Korean politicians say they've been left in the dark about the investigation. The legislature also has not been allowed to see the full report by the investigative committee, only a five-page synopsis.
The Cheonan, a 1,200-ton corvette, sank the night of March 26 about 12 miles off North Korea. The first report issued by Yonhap, the official South Korean news agency, said the ship had been struck by a torpedo, but soon afterward the story changed to say the ship sank after being grounded on a reef.
Rear Adm. Thomas J. Eccles, the senior U.S. representative on the panel, said investigators considered all possibilities: a grounding, an internal explosion, a collision with a mine. But they concluded that the boat was sunk by a bubble-jet torpedo, which exploded underneath the vessel and didn't leave the usual signs of an explosion, he said.
"The pattern of damage was exactly aligned with that kind of weapon," Eccles said. "Torpedoes these days are designed to drive underneath the target and explode. They use the energy of their explosion to make a bubble that expands and contracts. It is designed to break the back of the ship."
South Koreans themselves appear to be confused. Polls show that more than 20 percent of the public doesn't believe North Korea sank the Cheonan.