A murder suspect who told police there may be additional victims of the gang that killed two Russian siblings and a Thai family of three has been placed under witness protection, according to an informed source.

The source said Chatchanan Paen-iam was being held in isolation at Najomtien police station in Sattahip district of Chon Buri and was under special protection for his own safety.

The 23-year-old, known as “Fluke”, had told police the gang accused of murdering five people may have also killed other people - not just the two young Russians and the Thai family, the source said.

Mr Chatchanan was questioned for more than three hours by Chon Buri's chief detective, Pol Col Pasakorn Paijit.

Police would contnue to interrogate Mr Chatchanan about the murders, about other possible suspects and about loan sharking and debt collection that might have led to the murder of the Thai family, the source said.

Mr Chatchanan is one of four arrested suspects in the alleged serial murders. The others include ex-convicts Thana "Pong" Kerdthong, 43, and Thongchai "Thong" Srinil, 39, who were apprehended in Sa Kaeo province on Friday.

Thana allegedly murdered Russian siblings Diana Nazimova, 22, and Roman Nazimova, 17, and the Thai family of three, including raping the 17-year-old Thai daughter.

The fourth arrested suspect is Atsadang Chuwong, 25.

Meanwhile, the Department of Corrections revealed that Thana had been jailed for seven years, seven months and 25 days for attempted murder and crimes related to firearms and drugs. He had been released from Rayong Prison on June 5.

Just before his release a committee of corrections, probation, administrative and health authorities proposed measures to prevent Thana returning to a life of crime. In January the Rayong Provincial Court approved the proposal and ordered it be implemented for two years after his release.

The measures included a ban on any dubious activity, quarterly reporting to a probation officer and attendance at a rehabilitation course run by probation officials, the Department of Corrections Department said.