A key suspect in the murder of former Australian Hells Angel bikie and underworld figure Wayne Rodney Schneider has fled Thailand, police say, citing Thai immigration records.

Thai authorities had issued a warrant for the arrest of 26-year-old Sydney man Antonio Bagnato on charges of conspiring to assault and detain Schneider whose naked and mutilated body was found in a grave a short drive from the villa where he was abducted in the Thai tourist city of Pattaya.

Mr Bagnato is also a former motorcycle gang member who was Schneider's partner in a Sydney fitness centre.

Both men had been renting houses in Pattaya, a popular destination for wanted Australians, crime gangs and sex tourists

Witnesses saw five masked gunmen bash Schneider unconscious and throw him into a pick-up truck outside his rented home shortly before dawn on Monday.

Blood and bullet casings were found at the villa when police arrived.

Thai police investigating the killing detained two people on Wednesday, hours after a GPS tracking device led them to a two metre deep grave in woodlands where they found Mr Schneider's body with a broken neck and serious facial injuries.

Police said a 21-year-old American man was arrested as he attempted to cross the border into Cambodia at Sa Kaeo, 245 kilometres from Bangkok.

Police also detained for questioning a woman they said was Mr Bagnato's Thai partner over the rental of a black Toyota pick-up truck that was used in the abduction.

The woman told police she did not know the vehicle would be used in the kidnapping.

Police said it was unlikely the body would have been found but for the GPS tracker that was fitted to the vehicle that had been rented from a business in Pattaya.

Police said the GPS signal indicated the killers spent two hours at the site.

A massive manhunt is underway for suspects who police believe are all foreigners.

Fairfax Media revealed former Victorian Comanchero president, Amad "Jay" Malkoun, who was once considered the state's most powerful bikie boss, was interviewed by Thai authorities as a witness to the abduction.

Attempts to contact Malkoun were unsuccessful.

Malkoun was quoted as saying he slept through the entire ordeal and only learnt Schneider was missing from the police.

Malkoun told the Bangkok Post he had been a guest in Schneider's villa since Saturday and met Bagnato at the villa. The three men had gone out drinking on Sunday but Malkoun went home early because he was feeling ill, the Post reported.

Malkoun said he spoke to Mr Schneider and the other man briefly when they returned to the house and continued drinking.

Thai police and Australian law enforcement agencies have been investigating Australian motorcycle gang members in Thailand who are believed to have extensive business interests in the country.

Thai police said they found paraphernalia for taking crystal methamphetamine inside the house Schneider had been sharing with other motorcycle gang members, according to reports in the Thai media.

About a month ago, Schneider reportedly arrived at the villa and paid about $5000 to rent the villa for six months.

Police said they have made contact with Schneider's Thai wife, who is in Dubai, which is also where Malkoun has spent most of the past two years.

A source in Melbourne said Schneider was cashed up at the time of the abduction after recently returning to Thailand with the proceeds of a large drug trafficking operation in Europe.

The source said Schneider's new bank balance was well known among Australian bikie gangs and that it was not the first time he had been stood over.

Schneider was a convicted drug trafficker who had also been charged with obstructing the Australian Crime Commission, as he failed to give evidence during a coercive hearing.

He had been a member of the Lone Wolf gang, and crossed to the Angels' Sydney chapter in acrimonious circumstances about 2008.

A court heard in 2010 that he had a Hells Angel tattoo on one arm, which covered an earlier Lone Wolf tattoo, and a tattoo in Old English lettering which read "Corruption" on the other.

Malkoun was the president of the Comanchero bikie gang in Melbourne when it was considered the state's most powerful, lucrative and dangerous.

He left Australia in mid-2013 for Dubai, handing the state presidency of the Comanchero to Mick Murray.

He remained state sergeant, or second-in-command, and intended to stay with his family in Dubai for less than six months.

It is unclear if he has returned to Victoria, which he considers home, in the past two years. His extended family are understood to still be based in Melbourne.

Police claim the Comancheros have gone from being the state's most powerful bikie gang to one that is struggling for members in the past year, as half their members – including Murray – have been arrested.

That rise to prominence occurred largely under Malkoun, who became state president in 2009.

Despite his vast reach in the underworld, including relationships with corrupt police and being the subject of at least two federal drug probes, Malkoun has been charged with only one crime in more than 25 years.

In 1989, he was convicted, along with his brother Elie, of trafficking heroin, and was sentenced to a minimum of 16 years' jail. At the time, it was the largest heroin trafficking operation in Victorian history.

Malkoun was recently spotted in Chechnya and was reported to have established a Comanchero chapter in Russia by recruiting heavily armed mercenaries.

He was also reportedly in Singapore and Sydney, where he was rumoured to be eyeing real estate.

Schneider spent 18 months on NSW's "most wanted" list over the shooting of a bouncer in 2007 although the charges were later dropped.

He was found with more than $200,000 in betting chips and plaques from Melbourne's Crown Casino in 2009 that were suspected of being the proceeds of crime.

Schneider had been living in Pattaya for about a month.

With Nino Bucci