The major players, the major plotline

For almost two years, special prosecutor Patrick Fitzgerald has led an investigation to determine whether anyone acted illegally when the identity of CIA agent Valerie Plame was made public. After hearing testimony from some of Washington's most powerful figures, a grand jury is expected to issue indictments today.

Here are some key questions about the case.

How did this affair begin?

At its heart lie questions about the Bush administration's case for war against Iraq. On Jan. 28, 2003, in his State of the Union address, President Bush included these 16 words: "The British government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa."

The implication was that Iraq was developing a nuclear-weapons program. But U.S. intelligence officials had by then expressed doubts about that claim. In July 2003, Joseph Wilson, a former ambassador to two African countries and Iraq, wrote an op-ed piece in The New York Times disputing Bush's statement.

The CIA, he wrote, sent him to Niger in 2002 to determine if Iraq had tried to buy uranium from Africa. He concluded no. One week after Wilson's piece appeared, syndicated columnist Robert Novak reported that Wilson's wife, Valerie Plame, worked as "an Agency operative on weapons of mass destruction."

At issue is whether Novak's government sources blew her cover as a CIA agent, in violation of the Intelligence Identities Protection Act of 1982.

That law aims to protect the identities of "certain United States undercover intelligence officers, agents, informants, and sources." Wilson has claimed that White House officials leaked his wife's CIA role to the press as revenge for his criticism of the president's case against Iraq. Others say the sources were merely steering journalists away from Wilson's allegations.

Why have two senior White House officials — Bush's top adviser, Karl Rove, and Vice Presidential Chief of Staff I. Lewis "Scooter" Libby — faced such intense scrutiny?

In grand-jury testimony, several journalists revealed that one or both men had spoken to them about Wilson's wife and her employment.

Toward the end of the investigation, it has become clear that Fitzgerald has focused more on possible charges of obstruction of justice, perjury and making false statements, rather than on laws prohibiting public revelation of a CIA official's undercover status. Rove testified four times and Libby twice.

How wide was the investigation?

As special prosecutor, Fitzgerald has the task of investigating the alleged unauthorized disclosure of a CIA employee's identity. The Department of Justice later clarified that he had authority to investigate any crimes committed in the course of the inquiry, such as perjury, obstruction of justice, destruction of evidence and intimidation of witnesses.

In all, three dozen people either appeared before the grand jury or were interviewed by the FBI or Fitzgerald. The special prosecutor interviewed both Bush and Vice President Dick Cheney last year, but not under oath.

Key individuals who testified late in the process include Cheney aides John Hannah, an expert on weapons of mass destruction, and David Wurmser, a Middle East adviser.

Among the press, Matt Cooper of Time magazine, Judith Miller of The New York Times, Glenn Kessler of The Washington Post and Tim Russert of NBC News all testified. Novak is widely assumed to have cooperated with prosecutors, though he has not commented publicly on the case.

What was Cheney's role?

Libby learned about Wilson's wife from his boss, the vice president, before her identity had been made public, according to notes Libby took during the conversation and which were described to The New York Times by lawyers involved in the case.

It is not illegal for Libby and Cheney to discuss classified information; they both have security clearance. But the Libby-Cheney conversation contradicts reports of Libby's testimony, in which he is said to have stated that he first learned of Wilson's wife, and her employment, from reporters.