A federal judge dismissed all charges against a former FBI (search) informant accused of being a Chinese double agent, saying federal prosecutors engaged in deliberate misconduct in the case.

U.S. District Judge Florence Marie Cooper (search) on Thursday said the government blocked Katrina Leung's access to a critical defense witness — retired FBI agent James J. Smith (search), who for years was Leung's lover.

Leung, a wealthy socialite from the Los Angeles suburb of San Marino, allegedly took classified documents from Smith's briefcase. She was not accused of transmitting them to China.

The judge said prosecutors purposely kept defense attorneys from contacting Smith as they prepared for Leung's trial. In doing so, Cooper said, prosecutors violated Leung's due process rights.

Smith was the longtime FBI "handler" for Leung, a naturalized U.S. citizen who was recruited 20 years ago to work for the FBI by gathering intelligence during her frequent business trips to China. Prosecutors claim she began working for China around 1990.

Smith has pleaded guilty to a single count of making a false statement about the affair and agreed to cooperate with the government. He had been accused of mishandling classified material and allowing it to fall into Leung's hands.

U.S. attorney's spokesman Thom Mrozek said prosecutors strongly disagree with the ruling but had not decided how to respond.

"While litigating this motion we argued the government did not prohibit Mr. Smith from speaking to Ms. Leung's attorneys if he chose to do so," he said.

The government could drop the case, ask Cooper to reconsider or take the issue to the 9th U.S. Circuit Court of Appeals.

Leung would have faced up to 14 years in prison had she been convicted of illegally copying and possessing national security papers that she intended to use, or could have used, to harm the interests of the United States.

Leung's lawyers, Janet Levine and John Vandevelde, said in a statement that "the courts have again made sure that truth and justice are not mere platitudes."

The judge was sharply critical of the conduct of Assistant U.S. Attorney Michael Emmick and Robert Wallace, senior trial counsel with the Department of Justice counterespionage section.

Wallace sent an e-mail to Emmick suggesting they could not trust Smith to be interviewed by the defense and abide by his agreement to protect classified information. It also suggested they would be giving the defense a strategic advantage.

"In the face of that e-mail, anything short of an admission and apology on the part of the government is difficult to imagine," the judge said.

Mrozek said Smith had not been secreted away to keep him from talking to Leung's defense. "He's not hidden anywhere," he said. "To my knowledge they never even asked to conduct an interview with him."