Washington (CNN) -- The one major problem for the Navy SEALs who killed Osama bin Laden was the crash of one of their helicopters.
It was no ordinary military chopper. Numerous aviation experts say they see several telltale signs of stealth technology in photos of what was left after the SEAL team tried to destroy the craft.
Some think it was a secret aircraft.
"Had this particular helicopter not crashed, we still would have no idea of its existence," said Gareth Jennings, the aviation desk editor for Jane's Defence Weekly.
Jennings and other aviation experts say the helicopter may have been a heavily modified version of the UH-60 Black Hawk, a mainstay of the military's helicopter fleet.
But it may include stealth technology developed for the now-canceled RAH-66 Comanche helicopter. That aircraft was designed to be an armed reconnaissance craft capable of carrying only two people.
Two of the aircraft were built for test flights before the Army canceled the program in 2004, not because of performance but because it needed money to upgrade existing helicopters. At the time, Les Brownlee, then acting secretary of the Army, said, "We will retain relevant technologies developed in the Comanche program."
At the same 2004 briefing about the cancellation of the Comanche, then-Army Chief of Staff Gen. Peter Schoomaker said, "much of what we've gained out of Comanche we can push forward into the tech base for future joint rotorcraft kinds of capabilities as we look further out."
The helicopter in question was left on the ground at the al Qaeda leader's compound during the raid early Monday.
The SEALs were able to destroy much of the main body of the helicopter when it became clear it couldn't fly. But the tail rotor assembly came down on the other side of the compound wall and was left largely intact deep inside Pakistan when the SEALs finished their mission.
Pakistani troops were seen hauling the wreckage away on trucks covered with tarps. The Department of Defense, which would not comment about any speculation about a "stealth helicopter," also wouldn't say whether it's asked Pakistan to give the wreckage back to the United States.
"Given the very strong defense ties that Pakistan and China currently have, I wouldn't be surprised at all to see this wreckage end up in Beijing," Jennings said.
"And that has to be of great concern to the U.S. Department of Defense, because with that technology, the Chinese or any third party could either incorporate that technology into their own aircraft or they can figure out ways to defeat that technology, thereby rending stealth technology like this largely useless in future operations," he said.
What makes the experts think the aircraft that crashed in Abbottabad was a secret "stealth helicopter?"
• "The first thing that stood out, and it may seem like a small thing, is the color scheme. Whereas most Black Hawk Army helicopters are painted olive green, this particular one is gray. Not just any gray; it's infrared-suppressant gray, and the purpose of the IR gray, as it's known, is to help reduce the vulnerability of the helicopter to ground-launched heat-seeking missile systems," Jennings told CNN Pentagon Correspondent Chris Lawrence.
• Photos from Abbottabad show that the chopper had a five-bladed tail rotor. "On a conventional Black Hawk, you have four blades. The addition of the extra rotor blades on the tail rotor hub reduces the acoustic signature of the helicopter there by making it hard to hear, giving the SEALs that extra few minutes to get over the compound before anyone on the ground quite knows what's going on," according to Jennings.
• Those five tail rotor blades are partially covered by a disk-like object that Jennings called a "hub-mounted vibration suppression system." He believes it provides more noise suppression and some possible protection for the tail rotor from bullets of shrapnel. And it's not typical on military helicopters. "No, I've never seen that on an operational helicopter before," Jennings said. But he added that a similar system was part of the Comanche helicopter design.
• The blades on that tail rotor also appear to be shorter and thinner than typical Black Hawk helicopter's blades. One former Army Black Hawk pilot, who asked not to be identified, said, "More blades and shorter blades means the helicopter would make less noise in flight."
It's not just the tail rotor blades that are different. "On the main rotor assembly that was actually destroyed by the SEAL team on the ground the blades themselves are threaded, which signify that these are carbon composite rotor blades as opposed to conventional metal rotor blades, which again signifies aspects of stealth technology that have been incorporated into this particular helicopter," Jennings said.
• Some photos show parts of the helicopter appear similar to non-secret stealth aircraft. "What's left of the tail section of that helicopter, the shape of the fuselage, it's canted. It's angled. It's a shape that's synonymous with fixed-wing stealth fighters such as the F-22, the F-35. Essentially, it's designed to defeat radar. If you eliminate right angles in an aircraft design, radar waves can't bounce back," Jennings said.
CNN'S Chris Lawrence contributed to this article.