The trial of Russia's richest man got underway in earnest Thursday as prosecutors outlined fraud and tax evasion charges against oil tycoon Mikhail Khodorkovsky and he responded with a plea of not guilty from inside a metal cage in the courtroom.

"I have understood the accusation presented," he told a three-judge panel. "I have understood what I am charged with. I would like to express my attitude when there is an opportunity to do that. I plead not guilty on all counts."

The day's events in the Moscow courtroom moved the long-running case into the trial phase nearly nine months after Khodorkovsky was arrested at gunpoint by masked commandos who stormed his private plane at a Siberian airport. For the first time, prosecutors and defense attorneys progressed beyond preliminary motions into the substance of a case that could send the defendant to prison for 10 years.

The trial has captivated much of Moscow and is widely considered to be a touchstone of where Russia is headed. Authorities portray it as a crackdown on business leaders who bilked the nation during the sale of state assets in the 1990s. Critics see it as retribution against a powerful rival to President Vladimir Putin.

The trial is proceeding in parallel with a civil tax case against Khodorkovsky's Yukos Oil Co., Russia's largest oil producer. The state has begun moving to confiscate assets as compensation for a back tax claim, seizing share registries of Yukos production subsidiaries this week. The registries contain ownership data.

On Thursday, the company began paying the first $1.3 billion of the nearly $7 billion the government has demanded, in hopes of forestalling bankruptcy or dismemberment.

In the Moscow courtroom Thursday, prosecutor Dmitri Shokhin spent most of the day reading aloud the indictments against Khodorkovsky and his billionaire partner and co-defendant, Platon Lebedev, in a monotonous recitation that left many people yawning or dozing. Khodorkovsky at one point began reading a newspaper, while Lebedev worked on a crossword puzzle.

The charges stem from the 1994 privatization of a 20 percent share in a fertilizer company called Apatit and subsequent allegations that the two defendants avoided paying hundreds of millions of dollars in taxes. Shokhin accused Khodorkovsky of creating an "organized criminal group" intent on defrauding the state. "They wished to bring harm to the government," he said.

Khodorkovsky and Lebedev will respond in more depth to the charges Friday. "They're heavy charges," defense attorney Anton Drel said in an interview. "From the point of view of the evidence, all the defense lawyers think we have much more serious arguments of our clients' innocence."

Asked during a break to predict the verdict, Khodorkovsky's father, Boris, said, "We already know what it will be." Later, as the indictment was being read, he whispered his amazement at the charges. "An organized criminal group!" he said sarcastically. "I told my son, 'You must be really cool since you managed to commit so much crime in such a short period of time.' "

In customary trial cage, Mikhail Khodorkovsky asserts innocence.