Bangkok: The hunt for those behind the Bangkok shrine blast narrowed Monday as police revealed they have two new suspects after more bomb-making paraphernalia was found in a suburban apartment.
But two weeks after the unprecedented attack brought carnage to the city`s commercial centre, the motive for it remains shrouded in mystery.
The bomb that hit the Erawan shrine on August 17 was Thailand`s worst single mass-casualty attack. It killed 20 people, the majority of them ethnic Chinese tourists from across Asia.
Suspicion has alternated between Thailand`s bitter political rivals, organised criminal gangs, Islamist militants, rebels in the kingdom`s strife-torn south and sympathisers of refugees from China`s Uighur minority.
Thailand recently deported more than 100 Uighurs to China, enraging supporters of the minority who allege they face torture and repression.
Police are now seeking a Thai woman and an unidentified man after bomb-making materials were discovered over the weekend in an apartment in the Minburi suburb.
Investigators believe it was used as a hideout by the network that carried out the attack.
"We found fertiliser bags, watches, radio controls -- parts to make bombs and electric charges," said national police spokesman Prawut Thavornsiri. "We are confident they are the same group."
Police detained an unidentified foreign man on Saturday morning at another flat nearby, where detonators, industrial pipes and ball bearings were found.
In a televised broadcast Prawut displayed a photograph of the wanted Thai woman, taken from an official identity card, showing her wearing a black hijab.
He named her as 26-year-old Wanna Suansan -- also known by the Muslim name Misaloh -- the first time a suspect in the bombing probe has been identified.
A sketch of an unidentified man with a moustache was also broadcast.
Prawut did not give details of when the raid took place but added that the type of fertiliser found was urea-based.
Urea nitrate is commonly used in homemade bombs.No group has claimed responsibility for the attack, allowing speculation to fill the information gap with the ruling junta and police at times appearing to contradict each other.
Authorities have been at pains to play down any suggestion the attack was launched by international terrorists or targeted Chinese visitors, in a nation where tourism represents nearly 10 percent of the economy.
On Saturday police said the only suspect in custody, whom pictures showed was thin with heavy stubble, was part of a crime group who helped illegal migrants obtain counterfeit documents -- and that the bomb attack on the shrine was retaliation for a recent crackdown on their lucrative trade.
But some analysts have poured cold water on the theory.
"If it was linked to organised crime, where`s the profit motive? How does killing 20 innocent civilians help your business?" Zachary Abuza, an expert on Southeast Asian militant groups, told AFP.
Analysts have speculated the blast, which has not been claimed by any group, could have been motivated by revenge over Thailand`s recent deportation of the ethnic Uighurs to China.
The ruling junta, which has pegged its legitimacy to upholding security and reviving the flagging economy, may have pushed the police into "unsubstantiated hypotheses", Abuza added.
Media accompanied police during a search of multiple flats in Minburi on Sunday but no items were shown to the press and there was no announcement that evidence had been discovered.
The area is near to Nong Chok, another suburb where the unidentified foreigner was arrested on Saturday.
Both districts are mixed suburbs with significant Muslim populations.
Police say they are working with "several embassies" to try to ascertain the identity of the man, who is being held in military custody.
Officials initially said he was not cooperating with his interrogators as they brought in multiple translators -- including an English speaker.
But on Monday police chief Somyot Poompanmoung told reporters the suspect`s interrogation had yielded "very useful" information.
In a televised briefing on Monday, a junta spokesman said authorities had "not ruled out any scenarios".