For air traffic controllers, the morning of Sept. 11, 2001 started off like many others, until a curious voice came over the airwaves at 8:24 a.m.
"If you try to make any move, you're endangering yourself and the airplane," the voice said. "Just stay quiet."
Boston control tower officials had just overheard 9/11 hijacker Mohamed Atta in the first of what would be a litany of terrifying transmissions -- most between stunned air traffic controllers -- that would be sent through the morning as four planes were hijacked in the worst terror attack in U.S. history.
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The chilling messages are part of a recently released "audio monograph," the most complete collection yet of audio transmissions from the morning of Sept. 11, 2001, compiled first by the 9/11 Commission and completed by Rutgers Law Review.
Moments after Atta's message, the flight attendant on the plane, Betty Ong, called the American Airlines operations desk.
"The cockpit's not answering. Somebody's stabbed in business class," she said calmly. "I don't know. I think we're being hijacked."
Just over 20 minutes later, American flight 11 slammed into the North Tower of the World Trade Center. Soon after, air traffic controllers at Newark International Airport in New Jersey could see another plane, United flight 175, closing in.
"Another one just hit the building," a controller said.
"The building just came apart," said another.
From there, drama shifted to Washington, D.C., were American flight 77 was spotted on radar just outside the capital.
"I said, 'Oh my God. It looks like he's headed to the White House,'" air traffic controller Danielle O'Brien recalled. At 9:37 a.m., American flight 77 veered away from the White House and instead hit the Pentagon.
Then, controllers in Cleveland realized a fourth flight, United 93, had also been hijacked. Another aircraft spotted the plane, rocking its wings -- presumably an effort by the hijackers to keep passengers from storming the cockpit.
"[He] was waving his wings as he went past... they don't quite know what that means," a controller said then.
Three minutes later, at 10:03 a.m., United 93 crashed in a field in Shanksville, Penn. Approximately 30 minutes later, at least eight fighter jets were scrambled and pilots received orders to shoot down any more hijacked planes.
"[The] Vice President has cleared us to intercept tracks of interest and shoot them down if they do not respond," the mission crew commander said.
Those shoot down orders, of course, came after all the hijacked planes had already crashed. Instead, the U.S. military nearly shot down a civilian aircraft over Alaska which did not respond to air traffic control orders.