The family of a Thai man whose body was found dumped on the side of a busy Sydney road this month is asking the Royal Thai Police (RTP) to send Australian police his fingerprints so the body can be returned for funeral rites.

One of the relatives of Wachira "Mario" Phetmang, 33, told the Bangkok Post that she contacted the Royal Thai Consulate-General in Sydney two weeks ago to help them get in contact with the RTP via the Ministry of Foreign Affairs in Bangkok but still has not received a reply.

"The Australian police told us that his fingerprints are very important. They need to check that they match those on the body," said the woman, who declined to be named.

"If enough details correlate and the fingerprints are from the same person, they will ask the court to return his body to our family for funeral rites. We want Thai police to do this as quickly as possible," she added.

Ministry of Foreign Affairs spokesperson Busadee Santipitaks said on Wednesday that the ministry was working on the matter.

Wachira was last seen entering a South Hurstville petrol station in southern Sydney on May 25. His body was later discovered wrapped in plasticin a rain culvert next to Homebush Bay Drive, according to Australia's 9News.

After a forensic investigation, police confirmed he was Wachira, who had been living in Hurstville.

CCTV footage has since been released showing him at a service station on King Georges Road, along with a silver 2004 Hyundai Terracan registered in Victoria. The vehicle is not believed to have been owned by the dead man and has not yet been located.

Detective Superintendent Scott Cook from the NSW Police Homicide Squad told the media that Wachira was found wrapped in plastic and a mattress protector. He was bound and gagged and had been beaten.

NSW police have since confirmed that a postmortem revealed the cause of death to be blunt-force trauma linked to a serious assault.

"I would call upon any member of the public who knows anything about Mario's whereabouts between May 25 and June 6 to come forward and provide police with information," the police said.

Possible links to organised crime and drugs are also suspected.