The fingerprints of a foreign man arrested on Tuesday over the deadly Bangkok blast match those found on bomb-making items discovered at a flat over the weekend in Nong Chok district.
Police spokesman Pol Gen Prawut Thavornsiri said in a televised special programme that the man's fingerprints were found on a bottle containing bomb materials found in a room at the flat police raided.
He was referring to the second suspect who was arrested in Sa Kaew province.
"We can confirm that this man is directly involved with the bomb material," he added.
Found in the flat included bomb-making paraphernalia and dozens of fake Turkish passports. So far two men were detained over the bomb attack that killed 20 people and injured many others on August 17.
Prawut had refused to confirm the two men's nationalities. They believe both used fake identity documents and are liasing with embassies to ascertain their true nationalities.
Agence France Presse reported that on Wednesday, incoming police chief Pol Gen Chakthip Chaijinda said that a senior officer said the man arrested on Tuesday was talking to interrogators through an interpreter.
"He speaks Turkey's language," he told reporters, without specifying whether the language was Turkish or part of the wider Turkic family.
Asked whether the detainee was a Uighur, Chaktip said, "The passport says so. But we have to wait for confirmation."
Chaktip said the man was insisting on his innocence during his interrogation.