Thai police said they arrested a foreigner on Saturday who matched the description of a man who left a bag at the site of a Bangkok blast that killed 20 people nearly two weeks ago.
Police raided a decaying four-storey apartment block in a suburb of the capital and found "multiple" fake passports and bomb-making materials they said may have been used in the Aug. 17 bombing at a Hindu shrine, the deadliest in the country's history.
The suspect was a 28-year-old foreign man who had been in Thailand since January last year. He was being held at a military facility on charges of possessing illegal explosives and had admitted the passports were fake, police said.
"It's unlikely to be terrorism," Police chief Somyot Pumpanmuang told a news conference. "It's not an international terrorist act," he said of the attack.
Somyot did not explain how police had come to that conclusion, but said the motive was "taking personal revenge for his comrades". He did not elaborate.
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The bomb tore through the crowded Erawan Shrine, one of the country's top tourist attractions and close to several of Bangkok's most luxurious hotels and biggest shopping malls.
Among the dead were 14 foreigners, seven from mainland China and Hong Kong, in an attack the military government said was intended as a strike at Thailand's ailing economy. Scores of people were wounded.
Police have found few clues to the mystery of who masterminded the devastating attack.
No group has claimed responsibility and speculation has focused on who has motive and capability, pointing to southern ethnic Malay separatists, opponents of the junta, international extremists or sympathisers of Uighur Muslims, of which Thailand forcibly repatriated more than 100 to China last month.
Many of the minority Uighurs from China's far west have sought passage via Southeast Asia to Turkey. Thai police on Thursday said they were looking into recent arrivals from Turkey as part of their bomb probe.
National police spokesman Prawut Thavornsiri said more people were being sought and evidence pointed to the suspect's involvement in a second bomb a day later in the city's Sathorn area, which caused no damage.
"We found he's connected to both Bangkok blasts," Prawut said. "We believe the perpetrators are from the same group."
Prawut said the man detained "looks like" the prime suspect, who is a young man with shaggy dark hair and yellow shirt seen on grainy closed-circuit television footage dropping off a backpack and casually leaving the scene before the bomb went off.
Television showed still images of bags full of what appeared to be bomb-making materials seized at an apartment in Bangkok's Nong Chok district, which has a Muslim community and is close to mosques and Halal restaurants.
A rescue worker and policeman at the scene of the raid told Reuters the suspect had rented four apartments on the same floor.
Many Muslims lived in the area, according to second floor resident Khantree Srisombat, who said tenants of Middle Eastern appearance had rented rooms in the building, which cost as little as 2,000 baht ($56) a month.
"I'd seen him (the suspect) around... "I'd only seen him go into his room once," he said.
About the siezure of explosives there, he said: "I was quite afraid at first. Now I feel safe because police have cleared it away."
Police released photographs of the suspect, barefoot, hands behind his back, with a beard and hair shaved short. An image of a Turkish passport was shown on television with a photograph that appeared to be of the same man. Police indicated the passport was fake.
Police have been criticised over their conduct of the investigation. Reuters reporters on Friday found the authorities had not checked some CCTV footage
taken minutes after the blast, which featured a man dressed like the chief suspect.