"Our enemy is not each other but the terrorists who attacked us," Giuliani said in his opening statement to the panel. The former mayor acknowledged there were "terrible mistakes" made on Sept. 11 but attributed that to the unprecedented circumstances.
Giuliani's testimony came on the second day of hearings in New York by the Sept. 11 commission, created by Congress to examine what led to the attacks and advise on ways the country can avoid future attacks.
Giuliani appeared to be trying to deflect criticism from his former police and fire chiefs, who were widely hailed after the attacks but harshly criticized Tuesday for failing to communicate effectively on Sept. 11. Commissioner John Lehman called the lapses a scandal "not worthy of the Boy Scouts, let alone this great city."
Ex-fire commissioner Thomas Von Essen called Lehman's comments "despicable."
"The blame should clearly be directed at one source and one source alone: the terrorists who killed our loved ones," Giuliani said as family members of the victims broke into applause.
Giuliani went on to describe his actions and his feelings on Sept. 11, recounting a morning that began at breakfast with two friends and quickly turned into unimaginable horror. He recalled his final meetings with several victims, and he described the scene when the first tower collapsed.
"It first felt like an earthquake, and then it looked like a nuclear cloud," Giuliani said. As Giuliani remembered watching a man leap from around the 102nd floor, family members began to cry, clearly disturbed by the account.
Earlier Wednesday, the commission issued a report that said flaws in New York's emergency phone system deprived people in the twin towers of potentially lifesaving information. The findings were the second part of the most comprehensive probe to date of New York's response to the attacks.
The emergency phone system's operators and dispatchers did not know that fire chiefs had made decisions to evacuate the burning towers because the city did not have a way of relaying that information, the commission staff concluded.
With the buildings' public address systems out of service, workers inside the buildings dialed the 911 national emergency number for help but were not told to evacuate, according to report.
An unknown number of victims in the south tower might have had a better chance of survival if 911 operators had instructed them not to flee upward, where some found locked roof doors and no hope of escape, the report concluded.
"In several ways, the 911 system was not ready to cope with a major disaster," the report found.
Current Mayor Michael Bloomberg and Homeland Security Secretary Tom Ridge are also scheduled to testify Wednesday.
Tuesday's testimony focused largely on how fire and police officials worked, sometimes separately and sometimes together, and areas where information was not shared.
The miscommunication between the agencies was termed "a scandal" by Lehman, who then complained it was "not worthy of the Boy Scouts, let alone this great city."
Family members cheered when commission member Slade Gorton launched an aggressive line of questioning about the city's emergency system to Von Essen, former NYPD Commissioner Bernard Kerik and Richard Sheirer, former director of the New York Office of Emergency Management.
When the agency heads tried to defer to their successors, Gorton refused to let them.
The city's current police commissioner, Raymond Kelly, was asked if New York was now prepared to handle a chemical attack with 10,000 injuries. "I would say no," he replied.
Tuesday's hearing began with a commission report recounting how city officials were forced to make life-and-death decisions based on incomplete communications, leading to some of the deaths in the twin 110-story buildings.
The communication problems resulted in incidents such as the deaths of Port Authority workers told to wait for help on the 64th floor of one tower. Many of them died when the building collapsed.
Scores of family members were in the audience as the commission showed footage of both hijacked planes slamming into the 110-story towers, along with videotaped testimony from survivors. As the footage showed the towers' collapse, family members held hands and locked arms as they waited for the inevitable, many of them wiping tears from their eyes.
"For me, it was reliving what my mother heard, what she saw, what her last moments were," said Terry McGovern, whose mother died in the south tower.
Committee member Sam Casperson, in a minute-by-minute recounting of the second plane's crash into the World Trade Center, detailed how Port Authority workers were advised to wait for assistance on the 64th floor – and many of them died when the tower collapsed.
Communications breakdowns also prevented announcements to evacuate from reaching civilians in the building, Casperson said. One survivor of the attacks recounted calling 911 from the 44th floor of the south tower, only to be placed on hold twice.
Emergency 911 operators had a "lack of awareness" about what was happening at the twin towers, and were overwhelmed by the sheer volume of calls, Casperson said.
Officials also were asked about what they knew about terrorism threats in the months before Sept. 11.
The former director of the World Trade Center told the commission that he knew nothing of Osama bin Laden's terrorist network until the summer before the attacks, and was never privy to FBI intelligence that Islamic terrorists might hijack U.S. planes.
Alan Reiss said he first heard about bin Laden's al Qaeda network when ex-FBI agent John O'Neill was hired in the summer of 2001 as head of security at the trade center. O'Neill, who had hunted bin Laden for years, was one of the 2,749 people killed in the attack.
"I was aware of the plot against some of the other Port Authority tunnels and the U.N.," Reiss testified. "But we were never briefed" by the FBI.
Reiss also said he was more focused on fending off possible bioterrorism attacks such as anthrax, spending more than $100,000 to protect the building from such an assault.
"We felt this (anthrax) was the next coming wave," he said. "We had developed plans on how to isolate the air conditioning system and shut it down but never did we have a thought of what happened on 9-11."