Police continue to seek information about the backgrounds of two Russian women murdered in Pattaya, in spite of having arrested a suspect.

Chief investigator Lt-General Assawin Khwanmueng said diplomatic channels were assisting and could turn up a motive for the slayings.

Tatiana Tsimfer, 30, and Liubov Svirkova, 25, were shot dead by a Thai man about dawn as they sat in chairs on Jomtien Beach on February 24.

Anuchit Lamlert is in custody and has admitted killing the two in a robbery gone wrong.

But police want to know if either woman had personal or business disputes at home. They arrived in Thailand with a Russian tour party on February 16.

Assawin said a Russian man had told police Tsimfer confessed to marital problems.

Police now believe Anuchit did not kill the victims because he was hired or ordered to by another, he said.

Earlier information suggested Anuchit was hired by a Thai woman who was afraid her Russian husband would leave her for one of the victims whom the husband had association with after she visited his Pattaya tour company.

Police have arrested a third suspect, Monthol Bunmee, who owns the red Honda Wave motorcycle used by Anuchit in the killings.

Monthol has been charged with withholding information about a murder while Thinnakorn Meklee, the owner of the murder weapon, has been charged with illegal possession of a firearm.

Anuchit has shown police how he located the victims and attempted to rob them. He insists he shot the two when they screamed for help.

"I killed them because I was afraid they would remember my face," he said.

However, acting national police chief Seripisut Temiyavej still doubts the claim.

"There are inconsistencies in his confession and the evidence," Seripisut said during a visit to Pattaya on Saturday to question Anuchit.

"I believe the murder may be linked to a crime organisation and there may be other people behind it."

Seripisut told businessmen who met him on his trip it was time to clean up crime and mafia gangs deeply rooted in Pattaya.