A gang of robbers including four police was rounded up quickly after allegedly robbing two Lao nationals and their Thai business partner of 3.5 million baht in cash in Nakhon Phanom on Wednesday.

The suspects _ four policemen and a bank employee _ were rounded up only five hours after they allegedly held up the three victims on a road in Muang district.

Wearing policemen's trousers and carrying guns, the suspects allegedly forced the victims to hand over a bag containing cash they had just withdrawn from Kasikornbank's Muang district branch.

They then fled, allegedly taking one of the victims with them.

Somsak Wanwilai, 37, one of the Lao victims, and his Thai business partner Chaiwatphon Srisomsab, 50, told police they had just withdrawn the cash from Kasikornbank for their sawmill business in Laos. They said uniformed highway police stopped them on a road after leaving the bank.

A group of men pulled up in a car and told them to hand over the money bag, they said.

Mr Somsak said the robbers, who were carrying sidearms, took his younger brother, Sornchai Sriharaj, 36, in the car with them but freed him in front of Nakhon Phanom University soon after.

Immediately after learning of the robbery, Muang district police chief Pol Col Somneuk Mikhawan alerted Pol Maj Gen Churat Pan-ngao, commander of the provincial police, who was attending a police meeting in Pattaya.

The case finally reached national police chief Adul Saengsingkaew, who ordered a forward operation centre to be set up to handle it.

The centre was set up at a hotel in Muang district and brought together high-ranking officers.

The team put up checkpoints at border crossings to Laos in Mukdahan, Sakon Nakhon and Nakhon Phanom provinces as they questioned the victims for information about the robbery. The victims remembered the licence plate numbers of the cars used by the suspects. Officers tracked down the plates and identified the owners of the vehicles as police.

A check on the mobile phone records of one suspected member of the group showed he had contacted a bank employee and a border patrol policeman before the robbery. Pol Sgt Maj Ekachai Singthongchai, a highway policeman, was the first person to be arrested that evening.

He allegedly confessed to the robbery and gave information about the rest of the suspects, namely Pol Snr Sgt Maj Chadawut Nontkhamwong and Pol Snr Sgt Maj Jamnong Raksa, of the Highway Police, Pol Snr Sgt Narong Boonsinchai, of the 235th border patrol unit, and Phuvit Matlublao, a Kasikornbank employee at Muang district branch office.

Police said Mr Phuvit tipped off the other gang members that the money had been withdrawn.

The rest of the suspects were rounded up the same night. Police also found 3.5 million baht in cash, a pistol, five rounds of ammunition and five fake licence plates.

The four suspects denied any involvement in the robbery and vowed to fight the case in the court. The arrested police have been suspended and denied bail.

Pol Maj Gen Churat said the quick arrests resulted from cooperation between local police and the special operation centre.

He warned Lao nationals who come to withdraw money in Thailand to take special precautions. "They should come with friends and use more than one car for their own protection," he said.

Local police can provide special security services for them if they make a formal request, he said.

Contact Crime Track: crimetrack@bangkokpost.co.th