With reconstruction of its northeast coast underway and the damaged Fukushema nuclear plant under control after last month's tsunami (thanks to a few robots), the Japanese government has a new problem on its hands: Who quietly bought up nearly 10 percent of the plant's owner, national utility Tokyo Electric Power Company, when the stock price bottomed out two weeks ago? It might have been China.

Here's what happened: In the days after April 3, when TEPCO stock hit a low point and the company looked in danger of collapse, some entity started purchasing shares, ultimately buying some $600 million worth. It's the law in Japan that the owner of more than 5 percent of a publicly traded company must identify itself. There are also laws regulating foreign ownership of national security concerns. Whoever bought the TEPCO shares may be in violation of both of those laws, but until the government can prove that either has been broken, it can't launch an investigation into who might have broken them.

“They’re really, really pushing, trying to figure out who it was,” the [anonymous TEPCO] executive said of the regulators. “There’s somebody out there that holds a whale of a position, and structured the position in such a way that they don’t have to file” a mandatory disclosure.

Whoever sank hundreds of millions of dollars into the stock of an apparently failing company must have known something that everybody else didn't know. That's the theory of Japanese government regulators, anyway. And their fear is that it was China. However, the purchase orders came from Hong Kong, where most international business concerns have an office, so the purchases could have been made by anybody, including a Japanese investor. The stock is stable once more, and has risen to 467 yen today from a low of 292. Whether it was nerves of steel or inside information that drove somebody to buy up TEPCO stock, the gamble is paying off.