The foreigner arrested on suspicion of involvement in the deadly Aug 17 bombing is not cooperating with investigators, Thai police said.
As the 28-year-old is believed to be part of a network, the security agencies are expanding their hunt, based on mobile phone records, for others behind the blast that killed 20 people, 12 of them foreigners.
Yesterday, police searched another house in the Minburi district, close to where last Saturday's arrest took place, and found more bomb- making materials.
Security agencies downplayed the view held by many analysts that the blast was an act of international terrorism, saying that while no motive is being ruled out, the man who was arrested could be part of a people-smuggling group, acting in a feud.
"Security forces have always been reluctant to define something as terrorism, for domestic and international political reasons," said Professor Panitan Wattanayagorn, an adviser to the Deputy Prime Minister and Defence Minister, General Prawit Wongsuwan. "But there is no reason really not to call this terrorism," he acknowledged.
The suspect is being held for possessing illegal explosives. The haul found at his rented apartment was "staggering", said a source familiar with the investigation.
It included bomb-making materials such as pipes and fuses, ball bearings of the type used in the Aug 17 bomb and, according to a picture released by police, at least one explosive belt of the kind used in suicide bomb attacks. Stacks of fake Turkish passports were also found.
The source said the area where the suspect stayed, in the eastern outskirts of Bangkok, is a "staging point for Uighurs going to Malaysia or Turkey".
Of the foreigners killed on Aug 17, most were ethnic Chinese, though of different nationalities.
Security analysts speculate that the blast was a possible revenge attack by extremist Uighur elements in retaliation for Thailand's deportation last month of more than 100 Uighurs to China, which drew widespread outrage. The Uighurs are a Turkic-speaking Muslim minority in China's restive Xinjiang region.
At a press conference yesterday, a regime spokesman, Colonel Winthai Suvaree, made only a brief statement, then showed film clips of normal life and security officers checking people at border posts.
Analysts see the reluctance to use the "terrorism" label as aimed at protecting the local tourism sector.
China, too, is reluctant to link the blast to the Thai regime's acquiescence to its deportation requests, said one analyst who spoke on condition of anonymity. That would be admitting the deportation triggered a deadly backlash.
Said the source familiar with the investigation: "The facts speak for themselves - the scale, venue, the identity of those killed, the ethnic origin of the suspect. You don't have to be a terrorism expert to draw a conclusion."
Denial would only mislead the international community as well as Thailand's own security agencies, analysts warn.
"While Thailand should be commended for its initial breakthrough in the investigation, Bangkok must understand that the threat is persistent. No country, including Thailand, should deny the reality of the terrorist threat in South-east Asia," Singapore-based security specialist Rohan Gunaratna said.
"The impact of the terrorist attack in Bangkok needs to be harnessed... to strengthen their counter-terrorism capabilities. Rather than denying (that it is terrorism), it is in the long-term interests of Thailand and the region for Bangkok to engage (with)... counter-terrorism partners and address gaps and loopholes."
Deputy police chief Jakthip Chaijinda yesterday urged the media to "have confidence in the state officials, in the military, police".
"We are not going to risk our team, our nation and our country to (find) a scapegoat to close this case. There are many parties, many organisations watching," he said.
"Contrary to what critics say, the Thai police actually do a very good job; they are not flashy but they plod and prod," the source told The Straits Times. "There may be little understanding of the broader picture, but it is robust police work."
However, he warned that the bombing had changed the situation. "Now they must allow their professional, good officers - and there are many - to work free of any political interference. It is in the Thais' own interests that there should be no political spin."