What has the US Grand Jury been investigating?

A grand jury, overseen by special prosecutor Patrick Fitzgerald, has been investigating whether any United States government officials deliberately leaked to the press the name of a CIA agent in 2003 to discredit a critic of the Bush administration.

Who is the CIA agent whose name was leaked?

The agent is Valerie Plame. She is married to Joseph Wilson, a former diplomat. He was sent by the CIA to the west African state of Niger in 2002 to investigate pre-Iraq war reports that Iraq had tried to buy uranium there.

In July 2003 he wrote an article in The New York Times in which he accused the Bush administration of "twisting" pre-war intelligence to build the case for war, including its Niger/Iraq claims. Mr Wilson also implied that he went to Niger at the behest of the office of Dick Cheney, the US Vice-President.

How was Ms Plame's name made public?

A week after her husband's New York Times article, Robert Novak, a conservative columnist, reported that two senior administration officials told him that Mr Wilson had been sent to Niger by his wife - whom he referred to by her maiden name, Valerie Plame - "a CIA employee working on weapons of mass destruction".

Why was her name leaked and why did it lead to a criminal investigation?

After Mr Novak's column, Mr Wilson claimed his wife was a covert CIA agent and accused the White House of deliberately unmasking her to destroy her career and as retribution for his Iraq war criticism.

Republicans have always said that nobody in the White House knew Ms Plame was a CIA agent. They say that reporters, including Mr Novak, were simply briefed about her role in sending Mr Wilson to Niger to rebut his claims that it had been Mr Cheney's office that sent him to Niger.

But Mr Bush, amid a growing controversy, appointed Mr Fitzgerald in December 2003 to investigate. Mr Fitzgerald was originally tasked to investigate if any officials broke the 1982 Intelligence Identities Protection Act, which makes it a crime to knowingly reveal the identity of a covert agent. In February 2004 he sought and received written confirmation from the US Justice Department that his writ extended to bringing obstruction of justice and perjury charges.

Mr Bush said that he would fire anybody in his administration found to have "committed a crime" in relation to the affair.

Who was responsible for the leaking of Ms Plame's name?

The investigation soon focused on Karl Rove, Mr Bush's chief adviser, and Lewis "Scooter" Libby, Mr Cheney's Chief of Staff. Initially, the White House said that neither man was involved in Ms Plame's name being published.

But in June this year, two reporters who worked indirectly on the story were ordered to reveal the identity of their sources within the administration.

Time magazine's Matthew Cooper told the grand jury that Mr Rove and Mr Libby had told him about Ms Plame, but not by name.

Judith Miller, of The New York Times, refused to reveal her source and was jailed for 85 days. After her release she revealed that she had spoken to Mr Libby three times about Ms Plame, but again not by name.

Mr Novak has never commented publicly, but was never threatened with jail, and is assumed to have testified without complaint. Mr Rove is known to have talked to Mr Novak.

Testimony from Mr Rove and Mr Libby is known to have contradicted reporters' accounts. This week it emerged that Mr Libby first learnt about Ms Plame from Mr Cheney, and not from journalists, as he told the grand jury.

How bad is it for President Bush?

Very damaging. The indictment comes at a time of mounting sleaze allegations against Republicans, and as Mr Bush's approval ratings slump, amid concerns over Iraq, the aftermath of Hurricane Katrina, and his choice of Harriet Miers, his former personal lawyer, to the Supreme Court.

If Mr Rove should be indicted, Mr Bush will lose one of the most brilliant strategists in American history. Many analysts believe Mr Rove, the architect of Mr Bush's political rise from Texas governor to the White House, is indispensable.

Times Recommends

• UN may halt 400-year-old 'freedom of the seas'
• Where the Rosetta belongs can’t be set in stone
• Gas deal on hold, but Ukraine may pay in the end