Balkan military officials and other experts have told The Associated Press that in all likelihood, the Chinese from some of their technological know-how of an American F-117 Nighthawk, who was shot in Serbia in 1999.
Nighthawks were the first stealth fighter jets, planes, has been very difficult for radar to detect. But March 27, 1999, when NATO airstrikes in Serbia in the Kosovo war, has killed one Serb anti-aircraft missiles, one of the Nighthawks down. The pilot ejected and was rescued.
It was the first time one of the highly touted "invisible" fighters had already been affected. Pentagon believed a combination of clever tactics and sheer luck had given a Soviet-built SA-3 missile to bring down the jet.
The wreckage was scattered over a vast area of flat agricultural areas, and civilians gathered pieces - some the size of small cars - as souvenirs.
"At the time, told our intelligence reports of Chinese agents who roam the region, where the F-117 dissolved, the purchase of aircraft parts from local farmers," said Admiral Davor Domazet -Loso, military chief of staff during Croatia's war in Kosovo.
"We think the Chinese have used these materials to get a glimpse of the secret stealth technology ... and reverse engineer them, Domazet-Loso said in a telephone interview.
A senior Serbian military has confirmed that the wreckage was removed by memorabilia collectors, and some have ended up "in the hands of foreign troops down."
Efforts to obtain comments from the Chinese Ministry of Defense and the Pentagon failed.
hunter stealth multi-role China - known as Chengdu J-20 - made its maiden flight on January 11, revealing dramatic progress in its efforts to develop advanced military technologies.
Although the twin-engine J-20 is at least eight or nine years to enter the Air Force inventory, it can become a rival to American top-line F-22 Raptor, the Nighthawk's successor, and the only stealth fighter currently in service.
China launched the J-20 days before a visit to Beijing by Secretary of Defense, Robert Gates, has led some analysts to speculate that the timing was intended to demonstrate the growing power of armed forces China.
Despite high-profile visit of Chinese President Hu Jintao to the U.S. This week, many in Washington view China as an economic threat to the United States and concerns about Beijing's military power.
Some parts of the F-117 shot down wreck - such as the left wing with the U.S. Air Force insignia, canopy, ejection seat systems, the pilot's helmet and radio - is on display at Museum of Aviation in Belgrade.
"I do not know what happened to the rest of the plane," said Zoran Milicevic, deputy director of the museum. "Many delegations have visited in the past, including the Chinese, Russians and Americans ... but none has shown any interest in taking part of the jet. "
Zoran Kusovac, a consultant based in Rome said the military regime of former Serbian President Slobodan Milosevic regularly to share team captured the West with Chinese and Russian allies.
"They destroyed F-117 in mind the wish list for the Russians and Chinese," said Kusovac.
Russian Sukhoi T-50 stealth fighter prototype made its maiden flight last year and should enter service in about four years. It is likely that the Russians have collected knowledge Nighthawk stealth technology slaughtered.
The F-117, developed in great secrecy in the 1970, entered service in 1983.
Although it is completely invisible to radar, the shape and radar-absorbing coating detection very difficult. Radar section is further reduced because of the edge and out of the wings' structure consists of a honeycomb of color that do not reflect radar beams.
Kusovac said the idea of this important technology, particularly the machine a secret external radiation absorbent surface, it would significantly improve China's ability to stealth.
Alexander Huang of Tamkang University in Taipei said the J-20 was an important step forward for China. He described the argument-Domazet Loso's as "a logical evaluation."
"There is no greater source of origin of the stealth technology for the J-20," said Huang, an expert on air power in China. "The argument of Croatia Chief of Staff is lawful and can not be excluded. "
The Chinese are well known to the authors of industrial espionage in Western Europe and the U.S. administration has also become more aggressive in pursuing cases of Chinese espionage.
Western diplomats said China has maintained an intelligence post at their embassy in Belgrade during the Kosovo war. The building was hit by American bombers error in May, killing three people inside.
"What this means is that the Serbs and the Chinese shared their intelligence," said Alexander Neill, head of the Asia Security Programme at the Royal United Services Institute, a think tank of Defence in London. "It is very likely to share the technology they have recovered from the F-117, and it is possible that elements of the F-117 was obtained in China."