Aviation analysts say the remnants of the aircraft reveal they were part of one of the U.S. military's most closely-guarded secret: A stealth Black Hawk helicopter whose existence was only rumored. It had never been seen in public before.
"This is the first time we've seen an operation stealth helicopter," said Bill Sweetman, editor in chief of Defense Technology International magazine.
Analysts say photos that emerged on the Internet reveal it was no ordinary helicopter.
"One of the things that really stands out is they have a little disk over the motors, which is meant to baffle the sound and deny radar signature," said Daniel Goure of the think tank Lexington Institute.
Neighbors in the Abbottabad neighborhood where bin Laden's compound was located told ABC News they did not hear the helicopters Sunday night until they were directly overhead.
"It would be a vague sound," Goure said. "It might be the sound of a helicopter that was going in the opposite direction. This was designed so the time between hearing the helicopter and the SEALs dropping in on the compound was very short."
Residents near the bin Laden compound told ABC News that just before the stealth helicopters arrived, all electricity and cellphone service was knocked out and then came back on right after the choppers left.
One key to the chopper's stealth nature is a secret, heavily-coated, fabric-like material, which children in the neighborhood were seen collecting.
The Chinese military is known to have close relationships with the Pakistani military.
"There are probably people in the Pentagon tonight who are very concerned that pieces of the helicopter may be, even now, on their way to China, because we know that China is trying to make stealth aircraft," said ABC News consultant Richard Clarke.
The remaining large pieces of the secret U.S. helicopter were trucked away by Pakistani officials Wednesday to an unknown destination.
The Pentagon declined to comment on what analysts are saying about the stealth helicopters.
