BANGKOK • Thailand's police said yesterday that they would look into why criminal charges were dropped against the heir to the Red Bull energy drink fortune, who was accused of a 2012 hit-and-run killing of a police officer while driving a sports car.

The decision to drop the charges against Mr Vorayuth "Boss" Yoovidhya has stirred public anger about the country's entrenched culture of impunity for the rich and well-connected. The charges had included speeding, hit-and-run and reckless driving causing death.

The police had initially defended the decision, saying the attorney-general's office had sent them a letter in June informing them that the charges were being dropped.

Following a weekend of vitriol on Twitter which led to trending hashtags like #BoycottRedBull and #BossRedBull, the police announced the probe.

"A committee has been set up to ascertain the facts for transparency and fairness to all parties with regard to actions of the police, ensuring they were acting in accordance with the law and regulations," the police said in a statement.

The committee will report its findings in 15 days. The Office of the Attorney-General also said it would investigate the decision.

Red Bull has sought to distance itself from Mr Vorayuth, the grandson of the late Chaleo Yoovidhya, who created the energy drink Krating Daeng, or Red Bull.

Mr Vorayuth, who was 27 at the time, was accused of crashing his Ferrari into a policeman and dragging his body under the car for dozens of metres before fleeing the scene. He missed eight court summonses over the case before the authorities issued an arrest warrant five years after the incident. He later disappeared, apparently abroad, social media posts said.

The office of Prime Minister Prayut Chan-o-cha said on Sunday that news of the dropped case made him "uncomfortable" and stressed that he had never granted personal favours.

REUTERS, AGENCE FRANCE-PRESSE