Officials conducted surprise raids in camps for construction workers in the border province of Sa Kaew yesterday in a bid to track down a key suspect wanted for the recent Bangkok bombings.
The raids were conducted particularly in search of Aod Payungwongor, also known as Yongyut Pobkaew.
Rangers and police participating in the raids checked more than 500 workers to see if they matched the picture of Yongyut yesterday.
Authorities believe Yongyut might try to sneak out of the country by posing as a Cambodian construction worker.
Yongyut has drawn special attention from security agencies, as available information suggests he may have played a role not just in the recent Bangkok bombings, but two other bomb cases in the capital - one in 2010 and another in 2014.
Yesterday's operation failed to locate the man. However, officials managed to arrest 37 illegal workers. They also asked entrepreneurs to help watch out for Yongyut.
Two blasts occurred in Bangkok about seven weeks ago. An attack at the Erawan Shrine killed 20 people and injured more than 100 others on August 17. The following day, a second bomb erupted near Sathorn Pier, but without causing any casualty.
National Police Chief General Jakthip Chaijinda said yesterday three suspects arrested by Malaysian authorities had said they knew Zubair, the man who allegedly kicked the bag containing a bomb into the canal near Sathorn Pier.
"Ongoing investigation suggests Zubair had travelled to Thailand's South. But at this point, we can't say whether he is still in Thailand."
Jakthip added that police would seek arrest warrants for many more suspects for their alleged role in the Bangkok bombings. When asked about a foreigner who suspiciously walked into the Judge Advocate General's Department recently, Jakthip said police were looking into the matter.
Authorities have already arrested two suspects in connection with the blasts. Following the arrests, former prime minister Thaksin Shinawatra's son Panthongtae handed Bt 7million (S$275,000) to police as a reward that he promised to give to anyone with information leading to the apprehension of people behind the Erawan Shrine attack.
"Yes, the National Police Office has received that amount," Jakthip said yesterday. He said a committee would be established to divide money among units contributing to the efforts to solve the case - in the police, military or other agencies.