WASHINGTON Former White House aide I. Lewis "Scooter" Libby was sentenced to 2 1/2 years in prison Tuesday for lying and obstructing the CIA leak investigation. Libby, the former chief of staff to Vice President Dick Cheney, stood calmly before a packed courtroom as a federal judge said the evidence overwhelmingly proved his guilt. "People who occupy these types of positions, where they have the welfare and security of nation in their hands, have a special obligation to not do anything that might create a problem," U.S. District Judge Reggie B. Walton said. Walton did not set a date for Libby to report to prison. Though he saw no reason to let Libby remain free pending appeal, Walton said he would accept written arguments on the issue and rule later. Libby was convicted in March of lying and obstructing an investigation into the 2003 leak of CIA operative Valerie Plame's identity. The highest-ranking White House official convicted in a government scandal since the Iran-Contra affair, Libby has steadfastly maintained his innocence. "It is respectfully my hope that the court will consider, along with the jury verdict, my whole life," Libby said in brief remarks to the judge. Sitting with Libby's wife Harriet Grant during the sentencing were conservative commentators Mary Matalin, a former Cheney aide, and Victoria Toensing, a former deputy assistant attorney general during the Reagan administration. Walton fined Libby $250,000 and placed him on probation for two years following his release from prison. Walton did not immediately address whether Libby could remain free pending appeal. With letters of support from several former military commanders and White House and State Department officials, Libby asked for no jail time. His supporters cited a government career in which Libby helped win the Cold War and the first Gulf War. "He has fallen from public grace," defense attorney Theodore Wells said. "It is a tragic fall, a tragic fall." Special Prosecutor Patrick Fitzgerald called on Libby to serve up to three years in prison. "We need to make the statement that the truth matters ever so much," Fitzgerald said.