Police have released a gruesome photo showing how a Sydney man was shot in the head and neck with a nail gun 34 times.

27-year-old Chen Liu, who also went by the name of Anthony Liu, was found dead in marshland surrounding the Georges River in Sydney's south last year.

Police say the severely decomposed body was found just after 6:00pm (AEDT) on 1 November 2008 by two children, aged 9 and 14, who told their parents they had seen a body in Oatley Bay while on a canoeing trip.

Police say Mr Liu had been dead for 12 days before being discovered.

The Homicide Squad has been handling the case in conjunction with the Hurstville Local Area Command, forming Strike Force Renfree, but so far no arrests have been made.

They have now released an X-ray of the 27-year-old's skull and neck, which shows it was filled with 34 nails.

"Post-mortem examination results revealed Mr Liu was shot repeatedly to the head with a high-powered nail gun. Similar types of nail guns can fire nails up to 85 millimetres long," Detective Inspector Mark Newham of the Homicide Squad said in a statement.

The head of the Homicide Squad, Geoff Beresford, says the weapon has not been found.

"If anyone knows of a particular nail gun that has been stolen from them or from work premises, building sites, et cetera, we'd be grateful to hear that information," he said.

He says the victim had been in Australia for eight years, but has no family here.

"In 36 years of investigation, I've never come across a murder of this nature using a nail gun," he said.

"May I say it's a particularly brutal and vicious murder and we are seeking information from the public so we can bring this inquiry to a conclusion."

Detective Inspector Newham says information about the victim's car would be useful.

"Strike Force detectives are also appealing for information from anyone who might have seen Mr Liu's car in Rockdale or Connells Point around 19 October 2008," he said.

The car is described as a 2005 model blue Range Rover Sport four wheel drive, which police believe may have been used to dump Mr Liu's body in the marshland.

People with information are asked to contact Strike Force Renfree via Crime Stoppers on 1800 333 000, and police say all information will be treated in strict confidence.