The foreign man arrested on Saturday on suspicion of involvement in the Aug 17 bombings has refused to answer interrogators' questions on whether he played any role in them, police spokesman Prawut Thawornsiri said on Sunday.
Pol Lt Gen Prawut said deputy police chief Pol Gen Chakthip Chinda and his staff had gone to the 11th Infantry Regiment headquarters where the man is being detained after being arrested in an apartment in the Nong Chok area to question him.
The man would not comment on being involved in the Erawan Shrine and Sathorn pier bombings. His real name and nationality have not been established. Initially it was thought he was a Turk named Adem Karadag, 28, but his passport is believed to be fake, he said.
Interpreters of English and other languages are available to help in the interrogation.
Pol Lt Gen Prawut said it was believed many other people, some of whom were likely to Thai nationals, were involved in the crime.
Authorities had conducted a DNA test of the suspect and collected his belongings including clothes and shoes for further examination.
His mobile phone use would be traced. Bomb-making materials seized from the man's room had been sent to the Office of Police Forensic Science.
Pol Lt Gen Prawut said police were not ignoring any possible motive for the crime. One was that it might be an act of personal revenge after police had early smashed a counterfeit passport gang, he added.