Jigsaw: Scientists are closing on the identity of a sailor, below, from HMAS Sydney to being one of 50 crew members.

Jigsaw: Scientists are closing on the identity of a sailor, below, from HMAS Sydney to being one of 50 crew members. Photo: Fairfax Archives, Chris Moore

It's a mystery that has taken decades to unfold. Scientists need just one more piece of the jigsaw puzzle in the quest to identify the remains of the sailor whose body was retrieved from waters off Christmas Island, three-months after HMAS Sydney was sunk by the German raider HSK Kormoran in November 1941.

They don't know the sailor's name. He was one of 645 crew killed in what, 72 years on, remains Australia's greatest naval disaster.

His was the only body recovered and it took decades to confirm the bloated corpse found floating in a battered lifeboat off Christmas Island's Flying Fish Cove belonged to a HMAS Sydney sailor.

What scientists have been able to establish via analysis of his nuclear DNA at Adelaide University is that the man was of European ancestry, had red hair, blue eyes and pale skin. His skeleton shows he was tall for his generation, standing between 168.2 centimetres and 187.8 centimetres and was aged between 22 and 31. He was right-handed and had size-11 feet.

Isotope testing of teeth and bone samples conducted in Canada have revealed limestone traces that show he came from the east coast - most likely northern NSW or Queensland. He had a very high marine diet as a child, indicating he grew up on the coast rather than inland.

He also had two missing teeth and a complete set of wisdom teeth among a mouth crammed with filings - all nine of them gold. But it was unlikely he was an officer. Samples of fabric and press studs retrieved from his uniform and tested by Australian War Memorial researchers indicate he was wearing a navy-coloured boiler suit.

Such detailed information has allowed researchers to begin a process of elimination. And of the 645 crew lost when HMAS Sydney went down in the Indian Ocean, they are now targeting about 50 sailors.

''Here we have all the scientific evidence you would ever want and it's just a matter of tracing family down,'' deputy director of the University of Adelaide's centre for ancient DNA Jeremy Austin said. ''We have the answer sitting here, it's just finding that one person or two people in Australia who are related to this guy.''

Royal Australian Navy commander Greg Swinden has worked on the case since 2006. He said the sailor's distinctive teeth and dental work allowed forensic dentists Russell Lain and Matt Blenkin to exclude 330 crew after comparing the man's features with crew medical and enlistment records. His teeth could prove of further use, as they present such a distinct combination of fillings and missing teeth that a high quality photograph of a HMAS Sydney sailor smiling could help the dentists find their man.

The sailor's mitochondrial DNA has been extracted and successfully sequenced. This means researchers don't need a direct relation to make an identification, as long as the descendant can be traced through the female line of his family.

Professor Austin said the method had been successfully used to identify a number of high-profile cases including remains belonging to the Russian royal family, Ned Kelly and King Richard III.

Commander Swinden felt he knew the man well, which made him even more determined. ''We need to track a descendant down so we can take a DNA sample so that we can identify who this guy is and that will give a family closure,'' he said.

If you can help, contact greg.swinden@defence.gov.au