Former New York Times reporter Judith Miller testified Tuesday that former vice presidential aide I. Lewis "Scooter" Libby first discussed a CIA operative with her weeks before he told investigators he believed he first heard it from another reporter.

Miller spent 85 days in jail for refusing to cooperate with Special Prosecutor Patrick Fitzgerald's investigation into who leaked the CIA operative's identity to reporters. She had refused to disclose conversations she had with Libby.

Libby is charged with perjury and obstruction of justice. Fitzgerald says Libby discussed CIA officer Valerie Plame with reporters, then lied about those conversations.

Miller ultimately agreed to cooperate with authorities, saying Libby had given her permission to do so. She is a key witness in Fitzgerald's case because she describes two conversations with Libby regarding Plame before Libby told investigators he was surprised to learn about Plame from NBC reporter Tim Russert.

Miller testified Tuesday that Libby discussed the CIA officer on June 3, 2003. He said Wilson's wife worked for the "bureau," Miller recalled. She was confused about that at first, she said.

"Through the context of the discussion, I quickly determined it to be the CIA," she testified.

The discussion occurred amid a growing controversy about intelligence failures leading up to the war in Iraq. Plame's husband, former Ambassador Joseph Wilson, said he debunked some of the intelligence that was used to justify the war and said Vice President Dick Cheney should have known it.

Miller also discussed a second meeting with Libby, this one on July 8, 2003. She said Libby mentioned that Wilson's wife worked for a CIA division specializing in weapons of mass destruction.

Libby says his discussion with Russert occurred on July 10, 2003.

Journalism groups have criticized Fitzgerald for calling reporters as witnesses and demanding they discuss conversations with sources. Miller's notes likely will be used as evidence, and Fitzgerald is expected to call two other reporters — Russert and Matthew Cooper of Time magazine — during the trial.

Earlier Tuesday, David Addington, who served as Cheney's legal counsel during the CIA leak scandal, described a September 2003 meeting with Libby around the time that an investigation into the leak began.

"I just want to tell you, I didn't do it," Addington recalled Libby saying. "I didn't ask what the 'it' was," Addington added.

Fitzgerald hopes Addington's testimony will bolster his argument that Libby was worried about whether his conversations with reporters were improper and therefore lied to conceal them.