Thai authorities have not ruled out domestic politics as the motive behind the bomb attacks in Bangkok in the middle of last month, although the crackdown on human trafficking may also be the motive.

One of the suspects who is still at large, Yongyuth Pobkaew, is believed to have been involved in politically-motivated bomb attacks in 2010 and 2014, said Royal Thai Police Chief Police General Somyot Pumpanmuang.

"We have not defamed anyone because we have evidence in that direction and the facts obtained by the investigation officers," Somyot explained to a group of reporters, Monday.

He said the investigation team found evidences that linked Yongyuth who has no Thai identification number, to the bomb attacks near Erawan shrine and Sathorn pier in Bangkok last month.

Yongyuth is the link of the bomb attacks in August and two other bomb attacks during major Thai political conflicts, at Minburi district in Bangkok in 2014, and at Samanmeta mansion in Nonthaburi province in 2010, Somyot said, adding that further investigations were required to determine whether it is linked to domestic politics or not.

"That is why I have said this case is the case of two groups who have the same goal. One group could use another group, and thereafter they could gain the benefit together," he said.

Previously, there have been speculation that the bomb attacks have links to Thai politics and Thai authorities crackdown on human trafficking, but the often mentioned motives have been the deportation of Uighur to China earlier this year.

Meanwhile, Thai police spokesman Police Lieutenant General Prawuth Thavornsiri said in the attack this time, Yongyuth was in charge of providing support and preparation of bomb-making materials.

There are 15 suspects still on the run, comprising 13 foreigners and two Thais, Yongyuth and Wanna Suansan, a 26 year old Thai woman who married a Turkish man.