The murder of a tattooed Asian man whose body was found dumped in Melbourne's northwest was mostly likely a contract killing or related to drugs, police say.

His body was discovered by a former Victoria Police officer who noticed a bad smell while he was out walking with his wife and their dog at Park Orchards on the night of January 2, 2009.

It was found concealed under tree branches on a vacant lot on North Valley Road.

Detective Inspector John Potter says police believe the man was killed elsewhere and his body, which had blunt-force wounds to the head, was later dumped at the lot.

He says the man's body could have been there for up to one month before it was discovered.

"We have got a man who is dumped in a vacant block, brutally killed," he told reporters on Friday.

"It's either a contract killing or it's something to do with the illegal drug trade."

The man has a tattoo of a lion and a swooping eagle covering his whole back.

Det Insp Potter said police believed he was from somewhere in Asia and they had been in touch with Interpol and sent DNA profiling samples to overseas authorities in an effort to identify him.

He appealed to the public, particularly Melbourne's Asian community, to contact police if they may be able to help identify the man.

"Until we can establish who this man is we are unable to trace his movements at the time he died," Det Insp Potter said.

"So it's desperate that we hear from anyone that thinks they may know this man or may know somebody that can help us in this investigation."

Police believe the Asian man was aged between 25 and 40, was 170cm to 175cm tall and weighed about 48kg.

He was wearing red boardshorts and two diamond earrings in his left ear.