From the History Commons Groups blog:

A large number of new entries have been added to the Complete 9/11 Timeline at History Commons, covering a wide range of events relating to the 9/11 attacks. Entries cover, among other things, various warning signs of what was going to happen on September 11, 2001; the actions of John O'Neill, the FBI's top al-Qaeda expert; and new details of what happened on the day of 9/11.

CIA Was Initially Unsure Which Group Was Likely Behind the Attacks

Many entries describe events that occurred on September 11, 2001. Some of them describe the initial reactions and responses of government and military agencies to the attacks on the World Trade Center.