Thailand's police have said they consider the Erawan Shrine blast case solved, as they awarded themselves with cash, but will continue to investigate a potential domestic political angle to the bomb blast that killed 20 people on Aug 17 at the popular shrine in Bangkok.

At a press conference in Bangkok on Monday (Sept 28), Thai police chief Somyot Poompunmuang, who is serving his last days in office before retiring, reiterated that the bomb attack was revenge by a gang that was smuggling ethnic Uighurs out of China and had been damaged by a police crackdown.

But he said one of two Thai suspects in the case had also been involved in a bomb blast at an apartment in Nontahaburi on the outskirts of Bangkok in 2010.

"We have yet to establish these (political) links. It might have been a contract crime. A group might have hired another already bent on taking revenge to commit the crime, so both got what they wanted," he said.

The police have also again been awarded fat wads of cash in front of journalists for their efforts.

The 3 million baht (S$118,410) reward comprised donations from private businessmen as well as Gen Somyot's personal money, the chief said.

It was the second time "award" money has been given to police teams working on the case.

The Aug 17 rush-hour blast at the heart of downtown Bangkok was the deadliest in memory in Thailand, killing 20 people, including 12 foreigners.

The police have issued at least 17 arrest warrants, including for Chinese and Pakistani nationals, and have two people in custody.

Over the weekend, they said one of them, a foreigner whose nationality is still unclear but whose name has been given as Adem Karadag or Bilal Mohammed, had confessed to actually planting the bomb at the Erawan Shrine.

The blast at the apartment in Nonthaburi in October 2010 killed four people, including a man called Samai Wongsuwan, probably while he was assembling a bomb, the police said at the time.

Last year, the police arrested a Thai woman allegedly linked to the Nonthaburi case.

At the time, the government blamed the Nonthaburi blast on the "red shirts" who earlier that year, after months of protests against the government of then Premier Abhisit Vejjajiva, had been cowed by an army crackdown.

The red shirts, of the United Front for Democracy Against Dictatorship, were aligned with former premier Thaksin Shinawatra, who had been kicked out of of office by the military in 2006 on the back of royalist street protests against his rule.

The violence of the summer of 2010, which saw red shirts battling troops across central Bangkok, left over 90 dead - mostly civilian protesters.

nirmal@sph.com.sg