An immigration officer has been suspended for allegedly allowing foreign travellers to "re-enter" Thailand without them having to actually leave the country.
Immigration Bureau chief Surachate Hakparn on Wednesday identified the officer concerned only as Pol Snr Sgt Maj Witthayakorn Sarachan.
"The officer confessed to have provided entry stamps in return for 5,000 baht from each person," said Pol Lt Gen Surachate.
Samut Prakan-based Immigration Division 2 has filed a complaint over his wrongdoing with Don Muang police.
Investigators are looking further into the case, and are looking for other people who may have colluded with the officer in question.
It has prompted the transnational crime suppression centre to tighten its monitoring of foreign travellers.
Its operative unit, led by Pol Lt Gen Surachate, recently arrested five men who each owned multiple passports, complete with illegal immigration stamps.
According to investigators, some had different names and aliases, but used the same photos.
Olawale Raimi, 33, and Riches Ogbonna Onu, 44, from Nigeria, were arrested at a condominium in the city's Bang Kapi district and Arunothai housing estate in Chiang Mai's Chiang Dao district, respectively.
Tshepo Zuma, 37, from South Africa and Ouattara Ben Ibrahim, 21, from Ivory Coast were caught in Surat Thani.
Jonas Silva, 39, who holds a Guinea-Bissau passport, was caught by Immigration Division 1 officers in Bangkok.
A probe is currently under way to determine whether they were involved in criminal activities. Foreign criminals fleeing justice often choose Thailand to hide in.