The details of what happened to the four hijacked jetliners on Sept. 11, 2001, have been known for years, but when a prosecutor read a simple minute-by-minute account of the attacks, the jury deciding the fate of confessed Al Qaeda conspirator Zacarias Moussaoui hung on every word.

In a similar vein, the missed opportunities of the FBI and other agencies to prevent Sept. 11 have been known for years, but when FBI agents are forced to admit them on cross-examination, they seem fresh to the jury.

The jury has so far heard two days of testimony from FBI agents who provided a generic history of Al Qaeda and an accounting of the 19 hijackers' actions leading up to Sept. 11. Testimony continues Wednesday.

The government must establish that Moussaoui's actions resulted in death on Sept. 11. Prosecutors contend that if Moussaoui had not lied about his terrorist links and his flight training for a future attack, the government would have unraveled the Sept. 11 plot.

The blow-by-blow recitation Tuesday by prosecutor David Raskin of the hijackings — a stipulation of facts agreed to by both sides — did nothing to link Moussaoui to the plot, but nonetheless provided an emotional wallop.

Raskin quoted a radiophone call by flight attendant Amy Sweeney just before her plane became the first to strike the World Trade Center: "We are flying very very low," she told ground controllers. "We are flying way too low. ... Oh my God, we are way too low!" Then the phone went dead.

Moussaoui pumped his fist after hearing Raskin's account.

Moussaoui has pleaded guilty to conspiracy to hijack aircraft, but argues that he had nothing to do with Sept. 11 and was training for a possible future attack.

Defense attorneys argue that the FBI's incompetence and bureaucratic gridlock kept them from stopping the attacks, and a confession from Moussaoui would have changed nothing.

FBI agents have been forced to admit under cross-examination that the FBI knew years before Sept. 11 that Al Qaeda had plans to use planes as missiles to destroy prominent buildings.

They also had to acknowledge numerous missed opportunities in the months before Sept. 11 to catch two of the hijackers with terror links known to the government, even though the pair frequently used their own names in this country to rent cars, purchase plane tickets and even, once, to file a police report after getting mugged.