The sources quoted in The Washington Post say new evidence obtained by the panel indicates Osama bin Laden agreed to postpone the attacks after the situation was explained to him by suspected 9/11 mastermind Khalid Sheik Mohammed.
Khalid Sheik Mohammed has been in U.S. custody since March of last year and a source tells the Post that the new theory on what may have happened is based in part on interrogations of the suspected al Qaeda operative.
The commission's findings on the timing of the attacks is said to be in a draft report of the panel's findings - its final report isn't due until July 26 - and is expected to be discussed at the panel's final hearings, on Wednesday and Thursday this week.
The focus of this 12th and final hearing is the genesis of the plot from the perspective of the hijackers, and the national emergency response by the Federal Aviation Administration and U.S. air defenses on the day of the attacks.
"I want to see a clear timeline. What time did the FAA officially know a hijacking was taking place? What time did the president understand this was a hijacking? Why was there a delay in scrambling fighter jets?" said Mindy Kleinberg, whose husband, Alan, was killed in the collapse of the World Trade Center.
"I'm hoping at the end of this two-day hearing, we will have a picture of the defensive posture on Sept. 11," she said.
Some commissioners have said this week's hearings could be among the panel's most politically sensitive because they will explore communication gaps and decision-making by the nation's top leaders on the day of the 2001 attacks.
Some relatives of Sept. 11 victims have wondered whether military jets could have intercepted American Airlines Flight 77, which crashed into the Pentagon and killed 184 people, since that attack came more than 50 minutes after the first hijacked plane hit the World Trade Center.
The relatives also want to know why the chairman of the Joint Chiefs of Staff, Air Force Gen. Richard Myers, was not notified of the attacks until after the Pentagon was hit, and why President Bush didn't appear to take immediate action when he was notified. Mr. Bush was visiting with schoolchildren in Florida and was told of the attacks during a program.
Myers will testify Thursday.
As to the Sept. 11 plot, the relatives hope the commission will ask whether U.S. officials were justified in refusing to provide German authorities access to suspected Sept. 11 conspirator Ramzi Binalshibh, the Family Steering Committee for the 9/11 independent commission said in a statement.
In February, a German court, citing lack of evidence, acquitted Abdelghani Mzoudi, a longtime acquaintance of lead hijacker Mohammed Atta. The Justice Department had barred sworn testimony from Binalshibh and other al Qaeda prisoners on national security grounds.
Matthias Krauss, the German prosecutor who headed the investigation into the al Qaeda cell in Hamburg, Germany, will testify Wednesday.
The commission, which faces a July 26 deadline for its final report, is winding up a year and a half long investigation in which it interviewed more than 1,000 witnesses, including President Bush, and reviewed more than 2 million documents.