Police probing Thailand's deadliest bombing widened their net in the search for more suspects on Sunday after a foreigner was arrested and stacks of fake passports and bomb-making materials were found during a raid on a Bangkok apartment block.

The 28-year-old man, who has been in Thailand since January 2014, was detained on charges of possessing illegal explosives. Police have not revealed his identity or nationality.

The Aug. 17 bomb at Bangkok's Erawan Shrine, where Thais and Asian tourists flock each day, stunned Thailand.

Fourteen foreigners, seven from mainland China and Hong Kong, were among the 20 killed in an attack the ruling junta said was intended to cripple an already flagging economy.

Police have been criticized for an erratic investigation that had, until this weekend, uncovered few clues about who was behind the blast. No group has claimed responsibility.

Officials declined to say if the man arrested had provided new information, but deputy national police chief Chaktip Chaijinda told Thai television more suspects were being sought.

SUSPECT NOT ALONE

Police and residents in Bangkok's Nong Chok district said the suspect rented four apartments on the same floor of the rundown building.

A man and woman living on the same floor told Reuters the suspect did not live alone and they had seen a taller man with similar appearance entering and leaving several times each day. They had not seen the second man since Friday.

"We've seen two of them, frequently. One was the arrested man, but there's another, he's much taller," said the man, who requested anonymity because he feared for his safety.

The detained man was reclusive but always appeared focused and walked with intent on his rare forays outside. They said he was often seen on his knees praying outside the room.

"I still fear danger," the woman said. "We don't know if the other man has been arrested."

Speculation has focused on which groups could have motive and capability to carry out the bombing.

These have included southern ethnic Malay insurgents, opponents of the military government, foreign militant groups and sympathizers of Uighur Muslims. Thailand forcibly repatriated more than 100 Uighurs to China last month, prompting international outrage.

Many of the minority Uighurs from China's far west have sought passage to Turkey via Southeast Asia.

On Saturday, police indicated the person arrested was the prime suspect, a young man with shaggy dark hair who wore a yellow shirt and was picked out on security cameras dropping off a backpack at the shrine and leaving before the bomb went off.