Police are working with authorities in Turkey to track down a key suspect in last month's Erawan shrine and Sathon pier bombings after recent information suggested he had taken a flight to the country.
Meanwhile, Malaysian police on Monday confirmed they have arrested three suspects in connection with the Bangkok bombings.
National police spokesman Prawut Thavornsiri said a key suspect, Abudureheman Abudusataer, also known as Ishan, departed Dhaka, Bangladesh on a Jet Airways flight on Aug 30 before arriving in New Delhi, India. The information came from a joint investigation between Thai police and the Bangladeshi embassy in Thailand.
Mr Ishan then travelled to Abu Dhabi in the United Arab Emirates and finally Istanbul, Turkey.
He said the Turkish embassy and Thai authorities have been cooperating to gather information about Mr Ishan.
However, Pol Lt Gen Prawut said he was still unconvinced Mr Ishan was the mastermind because the money trail did not stop with him.
Meanwhile, the spokesman said two Malaysians and a Pakistani arrested in Malaysia played a role in helping suspected bomb cell members escape.
The arrests of the trio were carried out after a tip-off by Thai authorities, he said.
The three were thought to have smuggled people across the border, but no information has so far suggested they were involved in the blasts, the spokesman said.
His comment came after Malaysian police chief Khalid Abu Bakar confirmed yesterday that a Pakistani and two Malaysians -- a man and a woman -- were arrested a few days ago.
"These arrests were made following a tip-off received from our counterparts in Thailand," he told reporters.
Mr Khalid did not say where they were arrested or what the charges against them would be. "We are working together with our Thai counterparts. Let us investigate the matter first," he said.
Meanwhile, national police chief Pol Gen Somyot Poompunmuang yesterday denied speculation Thai police went to Malaysia to arrest the suspects.
"Thai police did not dispatch any officials to investigate this case in Malaysia," he said.
Pol Gen Somyot said a probe has found the bombings were an act of retaliation by a human trafficking network after the recent crackdown on people smuggling.
A Thai police source said the trio were connected to a network smuggling people into Malaysia through Sungai Kolok district of Narathiwat.
The source also said a man in a yellow shirt seen on CCTV planting a backpack at the Erawan shrine believed to contain a bomb shortly before the deadly blast on Aug 17 had fled to Pakistan.
The man has been identified, the source said, adding he had flown out of Thailand to Pakistan through normal channels. He used a Turkish passport but it has not been verified if it is real or fake.
Pakistani police confirmed the suspect had entered their country, the source said.
The source refused to name the suspect.
Thai police have so far arrested two suspects.
Adem Karadag, 28, also known as Bilal Mohammed, was arrested at his room at the Pool Anant apartment in Nong Chok district on Aug 29, while Yusufu Mieraili, 25, was later apprehended, according to the Thai military, in Sa Kaeo on Sept 1.
The pair are currently being detained at the 11th Military Circle after the Justice Ministry last week authorised the location to be used as a special remand facility.
Mr Karadag's lawyer, Chuchart Kanphai, said his client was a Turkish national and admitted to entering Thailand illegally.
He travelled from Vietnam and Laos before entering Thailand on Aug 24 this year with the help of a broker named Abdullah Abdulrahman, the lawyer said.
The lawyer said the broker took his client to stay at the Pool Anant apartment and told him to stay in the room.
He said his client was not involved with the bomb-making materials found at the apartment.
Mr Karadag intended to become a driver in Malaysia, Mr Chuchart said.
Speaking about security measures in the lead-up to China's National Day on Oct 1, Pol Gen Somyot said officers are prepared for the event.
Prime Minister Prayut Chan-o-cha has mentioned the importance of security for important figures, symbolic locations and tourist areas, Pol Gen Somyot said.
The police chief added that the Royal Thai Police are prepared to remove immigration officers who turn a blind eye to human trafficking in their jurisdictions.
The transfers will be made not only in response to the bombings, but also to illicit businesses such as smuggling Rohingya in the South, he said. Immigration police chief Sakda Chuenpakdi will deal with the issue and the transfers.