A former top aide to US President Bill Clinton has admitted taking classified documents from the National Archives.
Samuel Berger voiced regret over his "honest mistake"
Former national security adviser Samuel Berger pleaded guilty to removing copies of a classified memo before his testimony before the 9/11 Commission.
He acknowledged that he had destroyed three copies of the same document that dealt with terrorist plots to disrupt the millennium celebrations.
The offence carries a maximum one-year prison sentence and a $100,000 fine.
Mr Berger agreed to give up his security clearance and co-operate with the investigation.
He will be sentenced in July, the Associated Press news agency reports.
Mr Berger pleaded guilty before a court in Washington DC.
He testified in March 2004 before the commission, which examined all aspects of the 11 September 2001 attacks on New York and Washington.
As Mr Clinton's national security adviser, he was questioned about the Clinton administration's response to the al-Qaeda threat.
In preparation for his testimony, he reviewed thousands of pages of classified terrorism and security documents in a secure reading room at the National Archives in Washington.
The inquiry criticised US intelligence agencies for failures
It was during this work, according to Mr Berger and his lawyers, that he removed notes he had made about the anti-terror papers he consulted.
He admitted to removing and deliberately destroying some copies of a 1999 intelligence report.
Initially, Mr Berger said it was "an honest mistake" and apologised.
Mr Berger served as President Clinton's national security adviser from 1997 to 2001.
The Commission published its report in July last year.
It found the country's intelligence agencies failed to share information and were often engaged in bureaucratic competition.