NEW YORK — In the worst terrorist attack ever against the United States, hijackers struck at the preeminent symbols of the nation's wealth and might Tuesday, flying airliners into the World Trade Center and the Pentagon and killing or injuring thousands of people.
As a horrified nation watched on television, the twin towers of the World Trade Center in lower Manhattan collapsed into flaming rubble after two Boeing 767s rammed their upper stories. A third airliner, a Boeing 757, flattened one of the Pentagon's five sides.
A fourth jetliner crashed in western Pennsylvania. Authorities said the hijackers might have been trying to aim the plane at the presidential retreat at Camp David, Md., the Capitol or other targets in Washington.
The assaults, which stirred fear and anxiety across the country and evoked comparisons to Pearl Harbor, were carefully planned and coordinated, occurring within 50 minutes. No one claimed responsibility, but official suspicion quickly fell on Saudi fugitive Osama bin Laden. Unexplained was how the terrorists boarded the jets and overpowered the crews.
Federal law enforcement sources said the FBI conducted searches and served subpoenas, some in south Florida. One official said agents were investigating the possibility that some of the terrorists were pilots who had been trained "for this kind of action."
The FBI was sifting through hundreds of tips pouring into a toll-free hotline and a Web site and pursuing dozens of leads.
Addressing the nation Tuesday night, President Bush vowed to "find those responsible and bring them to justice." This country, he said, would retaliate against "those behind these evil acts" and any country that harbors them.
Altogether, the four downed planes carried 266 people. All were killed. Scores of people jumped to their deaths or died in fires and the collapsing superstructure at the Trade Center. New York Mayor Rudolph W. Giuliani said earliest reports counted 2,100 people injured, about 150 of them in critical condition.
Estimates of the death toll at the Pentagon ranged from 100 to 800.
At nightfall, more than nine hours after the attack, a 47-story annex to the 110-floor twin towers at the Trade Center collapsed as well. It too had caught fire, but by the time it fell, all of its occupants had been evacuated.
