Knowing All About it

On March 23, Condoleezza Rice was told that Bin Ladin was planning to attack the U.S. and he might use a truck bomb. People started getting alert when there was a repoert that Al Qaeda might be using aircrafts to attack the cities of London, Boston, and New York. Three months later, the government and agencies discovered that Al Qaeda is located in different parts of the Middle East and maybe they could be in Rome too. Agencies discovered that attack are imminent because there are people concentrated on the borders of the country. Bin Ladin and Al Qaeda told to the U.S. that they are planning a massive attack and they will follow the plan in short time.

"Clarke warned National Security Advisor Condoleezza Rice that domestic or foreign terrorists might use a truck bomb-their "weapon of choice"-on Pennsylvania Avenue." Rice was adviced that Al Qaeda will use a truck bomb and they actually used it, but in the World Trade Center instead of Pennsylvania Avenue.
"In early May, a walk-in to the FBI claimed there was a plan to launch attacks on London, Boston, and New York." They got information of the places that would be attacked and now, they knew barely what Al Qaeda meant to do.

Agencies and investigators got a lot of good information about the attacks that were being planned by the extremists. They knew the places that might be attacked and were these people were concentrated. These information was reliable and through spying, they got it from good sources and also from the actual extremist plans. If the U.S. knew almost everything, Why didn´t they stopped the attacks or improved security in important placessuch as airports?