THE American man dubbed the ''honeymoon killer'' should not face trial in the US despite widespread public anger at a plea deal that saw him serve just 18 months in an Australian jail, an international law expert says.

The state of Alabama intends to try Gabe Watson on charges of murder and kidnapping stemming from the death of his wife Tina during a scuba diving trip on the Great Barrier Reef in 2003.

The trial, scheduled for February, will be a violation of the principle of double jeopardy, under which a person cannot be prosecuted twice for the same offence or conduct, Dr Melanie O'Brien will tell a crime conference today.

Dr O'Brien, a research fellow with the ARC Centre of Excellence in Policing and Security at Griffith University, said Alabama authorities had attempted to circumvent the principle of double jeopardy by trying Watson for murder and kidnapping, rather than manslaughter.

''This second trial over in Alabama shouldn't be happening, regardless of the fact many people don't think justice was served by his 18 months [jail sentence],'' she said yesterday.

Under a plea deal with the Queensland Director of Public Prosecutions, Watson pleaded guilty to manslaughter and was deported to the US at the end of his imprisonment. He was extradited from California to his home state of Alabama for two capital murder offences.

In April, Watson's lawyers filed a motion to dismiss the charges, based in part on double jeopardy, and that it was a ''vindictive prosecution''. The judge did not rule on double jeopardy. However, he did find that the prosecution had the right to establish jurisdiction through evidence.

The trial, which is expected to last three weeks and call on a dozen Australians to give evidence, has twice been delayed because of budget cuts to courthouse security staff.

Watson, on bail and living with his second wife, will not be given the death penalty under a deal struck by the Australian government, but if found guilty, he faces a maximum life sentence without parole.

Dr O'Brien will present her paper at the Crime, Justice and Social Democracy conference at the Queensland University of Technology and hopes her arguments will be considered during the trial.