Born and bred in Hong Kong, Mitchell, 33, has a fascination about Hong Kong during the war years, particularly the Japanese occupation.

What he found was much more than he expected.

"The location was about three hours hike up a very difficult hill with no paths, so there was a lot of crashing through thick bush and getting scratched and tangled by plants," he says.

"While I didn't find the gun position, as I was leaving I noticed a large piece of metal, clearly very out of place with the surroundings. I recovered it as it looked like a piece of aircraft."

From bolt markings Mitchell identified it as part of an American plane. After numerous return trips he found more evidence of a plane crash. Using an 1949 aerial photo of the area and overlaying it on Google Earth with the GPS locations of the finds he had made he noticed a clear indentation in the land nearby.

"This eventually led me to a virgin crash site that was undisturbed since the war," he said. "While the main body of the plane was all aluminium and had melted in the subsequent fire and explosion, all of the heavy items such as the landing struts, engine part, propeller hub, armour plates and even an arrester hook were still intact."

Mitchell worked out that the plane was a TBM-Avenger. Six were lost that day over Hong Kong and action reports by other pilots said four of the TBMs crashed into the harbour, leaving just two unaccounted for.

It was the first time TBMs had been used in an attack on Hong Kong so there is no way it could have crashed earlier.

After further research Mitchell found that January 16, 1945, was the only day during the whole war that carrier-based aircraft were used on Hong Kong. Other bombing raids on the city by US aircraft were carried out from bases in mainland China and involved different planes.

Of the planes downed that day, two were involved in a mid-air collision and Mitchell believes it's one of these planes that he has uncovered.

Diary accounts from witnesses in Stanley prisoner-of-war camp back his claims, saying that two planes did collide and one fell where Mitchell found the plane parts.

One vivid account comes from the diary of George Gerards dated January 16, 1945:

"Today the first relay of bombers came over at 8.45am and kept up continuous bombing of Hong Kong and even near to us.

"Waves of bombers came over. We saw eight planes in one formation, and five in another just behind. They appeared like silver bullets in the sky when suddenly we saw the left-hand plane in the first formation swing over to the right and strike his companion.

"A terrific sheet of flame shot out and the first plane came lurching down, but the pilot bailed out and then the second plane made a big effort to get under control but to no avail, the fellow jumped but was caught in his incline and eventually crashed."

Having obtained all of the Navy Air mission reports involved in the raids on Hong Kong, Mitchell found that one of the two planes was flown by Lieutenant Richard Scobell with a crew of William P. Walton and John F. Franklin, while Lieutenant Richard Hunt was flying the other with a crew of Eugene Barrow and Louis Garhan.

Scobell had been shot down three months earlier during the battle of Leyte Gulf in the Philippines. His radioman was killed and he and his gunner spent more than 24 hours in a life raft before being picked up.

"All of the items I found at the site were consistent with the type of planes in the reports and could not be from any other plane - it was certainly a TBM-Avenger," Mitchell says.

But he still wasn't sure which of the two planes it was until he read more POW diary accounts.

"In the diaries they describe seeing two parachutes. One managed to deploy and was seen to come down safely, while sadly the other parachute from the second plane got tangled in the plane's rear wings and [Scobell] didn't manage to free himself before the plane hit the ground," Mitchell explains.

"From the accounts, I determined that the plane I found was the one in which the parachute did open safely."

He then set about trying to find out if any of the crew members survived.

He found a record that showed that the surviving pilot, Richard Hunt, was taken as a prisoner of war and transferred to a camp in Japan called Ofuna, where he died on February 25, 1945.

"Hunt died after being given an injection by the Japanese camp doctor. It's very possible he was murdered," says Mitchell, who is an engineer.

"He was very badly burned and also suffered a compound fracture to his left leg. I know that the wreck I found was that of Hunt's aircraft."

The witness accounts gave a vague description of where the second plane crashed and Mitchell has been searching for it for more than a year without success.

He does not want to give the exact location of the crash site, other than to say that it is in Tai Tam Country Park, because it might still contain the remains of crew members and he doesn't want scavengers to contaminate the site.

Mitchell has informed the US consulate in Hong Kong and the police about what he has uncovered. "I am 100 per cent certain of the facts, but it is all circumstantial and I will continue to look for more proof to put it beyond any doubt," he says.

If human remains are found, Mitchell will have to stop his project immediately and hand it over to the police.

That would also mean the American authorities could begin to conduct DNA analysis so the families of the airmen could be informed and a proper memorial service held.

But Mitchell's incredible story doesn't end here. Seven weeks ago he was out searching in the same area and stumbled across a 2,000-pound (907kg) bomb, from which the explosives and fuse had been removed.

He immediately informed the police, who collected the material. There were small bits of plane debris scattered around.

"From my research I knew that those two planes where carrying the only 2,000-pound bombs lost in HK during the war. All the debris at the site was also attributable to a TBM," he says.

Mitchell also identified other items from a TBM- Avenger, and recovered at least one full set of parachute fasteners and clips, valves and clips from a Mae West life jacket.

There were also some personal items, including a Philadelphia subway token used during the 1920s and a Zippo-style lighter.

"It's been quite a project and I have uncovered reams of information," Mitchell says.

"It is quite an amazing story, but hopefully as my search continues there's much more to be told yet."