In the most sweeping inquiry on the Iraq war, a panel investigating Britain's role in the conflict began questioning witnesses Tuesday in hearings that critics hope will humble ex-Prime Minister Tony Blair and expose alleged deception in the buildup to fighting.

The panel, which opened with a moment of silence for those who died, will question dozens of officials over several months — including military officials and spy agency chiefs. It will also seek evidence from ex-White House staff.

Among the most prominent witnesses will be Blair, who will be questioned on whether he secretly backed U.S. President George W. Bush plan's for invasion a year before Parliament authorized military involvement in 2003. Critics of the conflict hope to take Blair to task for publicly promoting a policy of containment even at a moment he considered regime change inevitable.