(Updated for closing stock prices)NEW YORK ( TheStreet) -- Four Rio Tinto ( RTP) executives held in dentention by Chinese authorities since last July unexpectedly admitted to accepting bribes as their trial began Monday in a Shanghai court, according to reports. The executives, all based in the Shanghai office of the Anglo-Australian mining giant, had been charged with taking bribes and stealing commercial secrets, a high-profile case that has tested diplomatic and business relations between Australia and China. According to reports, the admissions Monday involve only the bribery and not the industrial espionage charges. The lead defendant in the case is Stern Hu, an Australian citizen and Rio Tinto's one-time negotiator in its important contract talks with the biggest Chinese steelmakers over the price of iron ore. He pleaded guilty to accepting $1 million in bribes, the lawyer of another of the defendants told The New York Times Monday. But other statements from those who were in the courtroom indicate that Hu and the others -- all three are Chinese nationals -- will attempt to contest the alleged size the bribes as the trial continues. The four men were indicted in early February. Reporters were barred from the courtroom Monday, and details about the case remained murky even nine months after the initial arrests. The exact nature of the bribery wasn't entirely clear, for example. Apparently, Hu and the others took payouts from smaller steel mills in China in exchange for guaranteeing them access to iron ore, reports The Wall Street Journal, citing people who were inside the courtroom.