Thai authorities issued more arrest warrants on Monday and questioned two Indian men seen at an apartment block where explosives were seized, expanding a complex investigation into a deadly Bangkok bombing that remains shrouded in mystery.
The Indian nationals were not under arrest and were talking to military, police said, concerning their activities in the run-up to the Aug. 17 blast at the busy Hindu Erawan shrine, which killed 20 people and shook Thailand.
"CCTV footage showed the two men entering and leaving the room next door frequently, prior to the bomb blast," said a senior police official from Bangkok's Min Buri district.
He was referring to a room in one of two Bangkok properties where police raids have uncovered bomb-making materials.
Thai authorities were no closer to establishing a motive for the high-profile attack that killed 14 foreigners in one of the capital's busiest commercial areas.
Investigators have from the outset been focusing on a yellow-shirted man caught on security camera placing a rucksack at the shrine before the explosion.
No matches have been found for DNA taken from fragments of the backpack, a taxi and a banknote used by the suspect.
Police are questioning two foreigners arrested last month whose names and nationalities they still cannot confirm.
They have forensic evidence tying the two men to a stash of fake passports and bomb-making materials found in the city's Nong Chok area, but nothing connecting them to the shrine bombing.
Arrest warrants were issued on Monday for two foreigners linked to the same building, police said.
Some security experts have suggested the blast could have been a revenge attack by sympathisers of the mainly Turkic-speaking Uighur Muslims from China's Xinjiang province, where they suffer persecution.
Thailand faced international condemnation in July when it forcibly repatriated 109 Uighurs, many of whom seek passage to Turkey via Southeast Asia.
Among the evidence seized from the two suspects arrested was a Chinese passport stating Xinjiang as a birthplace, and a pile of Turkish passports. Police believe they could be fake.