US:A special prosecutor has accused vice-president Dick Cheney's former chief of staff of lying to federal investigators in an effort to conceal Mr Cheney's role in trying to discredit a former CIA officer and her husband, who was a critic of the war in Iraq.
Special prosecutor Patrick Fitzgerald said former vice-presidential chief of staff Lewis "Scooter" Libby repeatedly lied to federal agents investigating the leak of Valerie Plame's identity as a CIA officer.
Speaking on the first day of Mr Libby's trial for perjury, making false statements and obstruction of the leak investigation, Mr Fitzgerald said Mr Cheney had told his chief of staff that Ms Plame worked for the CIA.
Mr Fitzgerald said Mr Libby subsequently discussed the information with reporters. "But when the FBI and grand jury asked about what the defendant did, he made up a story. "How could we reach a point where the chief of staff for the vice-president was repeatedly lying to federal investigators? That's what this case is all about," he said.
Mr Fitzgerald said Mr Libby became the vice-president's point man in talking to the press to rebut Ms Plame's husband, a former ambassador who publicly raised doubts about President Bush's statements on Iraq's nuclear weapons programme.
Ms Plame's undercover status was revealed in the political crossfire between the administration, particularly the vice-president's office, and her husband Joseph Wilson.
Mr Libby's defence attorney said his client did not deliberately mislead investigators but preoccupied with national security issues, he forgot the sequence of events surrounding the disclosure of Ms Plame's identity.
Attorney Theodore Wells said Mr Libby complained to the vice- president in 2003 that the White House was making him a "sacrificial lamb" in an effort to protect Mr Bush's top adviser Karl Rove, who also spoke to reporters about the CIA agent's identity.
"They're trying to set me up. They want me to be the sacrificial lamb," Mr Wells said, recalling the conversation between Mr Libby and Mr Cheney. "I will not be sacrificed so Karl Rove can be protected."
Mr Libby, who faces five separate charges, could be imprisoned for up to 30 years - up to 10 years on the obstruction charge and up to five years on each of the others. Mr Cheney is expected to appear as a witness for the defence, becoming the first serving vice-president to testify in open court.