Panthongtae "Oak" Shinawatra has given police the 7-million-baht reward promised to them after they solved the Erawan shrine and Sathon pier bombings case.
The only son of Thaksin posted on his Facebook he had on Saturday given 5 million baht to police and 2 million to informants after suspects were arrested and the case was solved.
"I never have second thoughts about the 7-million-baht reward. I've always wanted to give it to boost officials' morale.
"But what bothers me is the attempt to implicate Thai nationals even though the foreign suspects had confessed. It's as if they were trying to hide something," he wrote.
Mr Panthongtae was referring to accusations by some high-ranking police officers and military spokesmen who said the bombings were politically motivated.
"It started when a government spokesman blamed it on politicians 'who lost interests' even when the smoke hadn't died down.
"Since then, authorities at different agencies have tried so hard to implicate Thais even though all evidence pointed to a foreign gang," he continued.
Such efforts put officials under enormous pressure as they feared the outcome of the case might be different from what the big bosses wanted, he said.
"Even today, when the suspects confessed they had chosen the two locations because there were a lot of Chinese tourists, we never know why [they targeted] the Chinese and why Thailand. That knowledge will help us solve the problem at the root. But this issue has never been touched as if they wanted to protect someone."
Mr Panthongtae was probably referring to former police chief Somyot Poompunmuang's reluctance to say the crime was linked to the deportation of Uighur Chinese earlier. Instead, he claimed it was the work of human traffickers who lost their business after a heavy police crackdown.
"The powers-that-be should be concerned about the losses of lives and be clear about the motive of the bombings so people feel relieved. Instead, they have tried to stress only one point — that Thais are involved," he wrote.
Apart from the Thai wife of a Turkish suspect, police last week said a Thai man was involved and he had previously been involved in two "politically motivated" bombings in Bangkok. Some of them said he was a red-shirt guard but others did not confirm it.
"Of course, when foreigners plant bombs in Thailand, Thais are involved. They hail Thai tuk-tuks. They hire Thai taxi motorcycles. They stay at Thai-owned apartments. They buy materials from Thai shops. They use Thai lawyers.
"So long as they bend over backward to implicate politicians, they will never find the real motive of the bombings."
Mr Panthongtae said he was willing to give the reward to the policemen who had worked straightforwardly and to the informants who helped find the suspects.
"But those who closed their eyes and ears and accused only politicians do not deserve even a single baht."