The official story has been that passengers on the United Airlines flight rushed the hijackers in an effort to prevent them from crashing the plane into a strategic target – possibly the U.S. Capitol.

During his surprise Christmas Eve trip to Iraq, Defense Secretary Donald Rumsfeld referred to the flight being shot down – long a suspicion because of the danger the flight posed to Washington landmarks and population centers.

Was it a slip of the tongue? Was it an error? Or was it the truth, finally being dropped on the public more than three years after the tragedy of the terrorist attacks that killed nearly 3,000?

Donald Rumsfeld

Here's what Rumsfeld said Friday: "I think all of us have a sense if we imagine the kind of world we would face if the people who bombed the mess hall in Mosul, or the people who did the bombing in Spain, or the people who attacked the United States in New York, shot down the plane over Pennsylvania and attacked the Pentagon, the people who cut off peoples' heads on television to intimidate, to frighten – indeed the word 'terrorized' is just that. Its purpose is to terrorize, to alter behavior, to make people be something other than that which they want to be."

Several eyewitnesses to the crash claim they saw a "military-type" plane flying around United Airlines Flight 93 when the hijacked passenger jet crashed – prompting the once-unthinkable question of whether the U.S. military shot down the plane.

Although the onboard struggle between hijackers and passengers – immortalized by the courageous "Let's roll" call to action by Todd Beamer – became one of the enduring memories of that disastrous day, the actual cause of Flight 93's crash, of the four hijacked jumbo jets, remains the most unclear.

Several residents in and around Shanksville, Pa., describing the crash as they saw it, claim to have seen a second plane – an unmarked military-style jet.

Well-founded uncertainly as to just what happened to Flight 93 is nothing new. Just three days after the worst terrorist attack in American history, on Sept. 14, 2001, The (Bergen County, N.J.) Record newspaper reported that five eyewitnesses reported seeing a second plane at the Flight 93 crash site.

That same day, reported the Record, FBI Special Agent William Crowley said investigators could not rule out that a second plane was nearby during the crash. He later said he had misspoken, dismissing rumors that a U.S. military jet had intercepted the plane before it could strike a target in Washington, D.C.

Although government officials insist there was never any pursuit of Flight 93, they were informed the flight was suspected of having been hijacked at 9:16 am, fully 50 minutes before the plane came down.

On the Sept. 16, 2001, edition of NBC's "Meet the Press," Vice President Dick Cheney, while not addressing Flight 93 specifically, spoke clearly to the administration's clear policy regarding shooting down hijacked jets.

Vice President Cheney: "Well, the – I suppose the toughest decision was this question of whether or not we would intercept incoming commercial aircraft."

NBC's Tim Russert: "And you decided?"

Cheney: "We decided to do it. We'd, in effect, put a flying combat air patrol up over the city; F-16s with an AWACS, which is an airborne radar system, and tanker support so they could stay up a long time ...

"It doesn't do any good to put up a combat air patrol if you don't give them instructions to act, if, in fact, they feel it's appropriate."

Russert: "So if the United States government became aware that a hijacked commercial airline[r] was destined for the White House or the Capitol, we would take the plane down?"

Cheney: "Yes. The president made the decision ... that if the plane would not divert ... as a last resort, our pilots were authorized to take them out. Now, people say, you know, that's a horrendous decision to make. Well, it is. You've got an airplane full of American citizens, civilians, captured by ... terrorists, headed and are you going to, in fact, shoot it down, obviously, and kill all those Americans on board?

"... It's a presidential-level decision, and the president made, I think, exactly the right call in this case, to say, I wished we'd had combat air patrol up over New York.'"