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 US 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. "We want to examine the evidence," said John Chilcot, the commission's chair. "We will approach our task in a way that is thorough, rigorous, fair and frank." Bereaved families and anti-war activists have long called for a comprehensive study to consider Britain's role in a conflict that left 179 British soldiers dead and triggered massive public protests. But some worry the hearings will do little to answer lingering doubts about Britain's rush to join the war. Led by a panel appointed by Prime Minister Gordon Brown, the inquiry won't apportion blame, or establish criminal or civil liability - only offer reprimand and recommendations in hopes mistakes won't be repeated in the future. In the United States, the 9/11 Commission examined some issues around prewar intelligence, and a Senate select committee identified failures in intelligence gathering in a July 2004 report on prewar intelligence assessments. But the Iraq inquiry is envisioned to be a comprehensive look at the war. Brown set up the inquiry to address public criticism of three key aspects of the conflict: the case made for war; the chaotic planning for the invasion; and the failure to prepare for reconstruction. Leaked military documents published Sunday disclosed that senior British military officers claim war plans were in place months before the March 2003 invasion, but were so badly drafted they left troops poorly equipped and ill-prepared. Some relatives of dead soldiers demanded the chance to question Blair when he gives evidence to the panel early next year - an idea rejected by the inquiry. Rose Gentle, whose 19-year-old son Gordon was killed in Iraq in 2004, said many bereaved parents will attend Blair's sessions. Many in Iraq praised the decision to hold the inquiry, saying that the US and British administrations lied when they invaded the country under the pretext searching for weapons of mass destruction. "There were no weapons of mass destruction as they alleged," said Rabie al-U'baidi, an Iraqi political analyst and writer. "This is a big lie and Tony Blair had (been) involved in driving it." Chilcot, a retired civil servant, heads the panel of five officials - who include a Winston Churchill biographer and an ex-British ambassador to Russia. Chilcot has acknowledged the study may not satisfy those who insist the war was unjustified and illegal. A final report won't be ready until the end of 2010, and may take longer if evidence presented is complex. "I make a commitment here that, once we get to our final report, we will not shy away from making criticisms where they are warranted," Chilcot said. Four government officials - including Michael Wood, an ex-legal adviser to Britain's Foreign Office, and Simon Webb, a former defense ministry policy director - were testifying Tuesday. Two previous studies into specific aspects of the conflict have been criticized as too timid. One cleared the government of blame for the death of David Kelly, a government weapons scientist who killed himself in 2003 after he was exposed as the source of a BBC report that accused Blair's office of "sexing up" prewar intelligence. A separate 2004 inquiry looked at intelligence on Iraq, clearing Blair's government but criticizing intelligence officials for relying on seriously flawed or unreliable sources.