BANGKOK (REUTERS) - Thai Prime Minister Prayut Chan-o-cha said on Wednesday (July 29) his government would ensure justice prevails over a deadly 2012 hit-and-run linked to the heir to the Red Bull energy drink fortune, amid public anger over the dropping of charges against him.

The Office of the Attorney-General and the national police dropped criminal charges against Mr Vorayuth "Boss" Yoovidhya last month, without providing a reason, stirring public outrage about Thailand's entrenched culture of impunity for the rich and well-connected.

Mr Vorayuth had missed eight summonses to appear in court in connection with the killing of policeman Wichien Klanprasert, whose body was dragged for dozens of metres under a Ferrari sports car owned by Mr Vorayuth, who was 27 at the time.

Authorities issued a warrant for his arrest five years after the incident and Mr Vorayuth later left the country. His current whereabouts is unknown.

Mr Prayut said a committee had been formed to look at what led to the case being dropped but it would not interfere in the work of the Attorney-General, police and court. The committee has 30 days to complete its task.

"This case is of great interest to the people and society, so we must find the truth to see where the problems are," he said.

"We must fix these problems to ensure justice in Thai society without dividing it along social class lines," he said.

The Office of the Attorney-General and police said they were also looking into what led to the case being dropped.

Mr Vorayuth had been accused of fleeing the scene of the crash.

A family driver initially tried to take the blame but was later charged with giving a false statement to police.

Police have said the old case against Mr Vorayuth had officially ended and could only be relaunched if relatives of the victim filed the case directly to a court, or if there were new witnesses or evidence.