"This is a very, very important part of history and we've got to tell it right," said Thomas Kean.
"As you read the report, you're going to have a pretty clear idea what wasn't done and what should have been done," he said. "This was not something that had to happen."
Appointed by the Bush administration, Kean, a former Republican governor of New Jersey, is now pointing fingers inside the administration and laying blame.
"There are people that, if I was doing the job, would certainly not be in the position they were in at that time because they failed. They simply failed," Kean said.
To find out who failed and why, the commission has navigated a political landmine, threatening a subpoena to gain access to the president's top-secret daily briefs. Those documents may shed light on one of the most controversial assertions of the Bush administration – that there was never any thought given to the idea that terrorists might fly an airplane into a building.
"I don't think anybody could have predicted that they would try to use an airplane as a missile, a hijacked airplane as a missile," said national security adviser Condoleeza Rice on May 16, 2002.
"How is it possible we have a national security advisor coming out and saying we had no idea they could use planes as weapons when we had FBI records from 1991 stating that this is a possibility," said Kristen Breitweiser, one of four New Jersey widows who lobbied Congress and the president to appoint the commission.
The widows want to know why various government agencies didn't connect the dots before Sept. 11, such as warnings from FBI offices in Minnesota and Arizona about suspicious student pilots.
"If you were to tell me that two years after the murder of my husband that we wouldn't have one question answered, I wouldn't believe it," Breitweiser said.
Kean admits the commission also has more questions than answers.
Asked whether we should at least know if people sitting in the decision-making spots on that critical day are still in those positions, Kean said, "Yes, the answer is yes. And we will."
Kean promises major revelations in public testimony beginning next month from top officials in the FBI, CIA, Defense Department, National Security Agency and, maybe, President Bush and former President Clinton.