Thai authorities have said Vorayuth Yoovidhya left on April 25, days before an arrest warrant was issued for him after he failed to show up to face charges.
Vorayuth Yoovidhya allegedly knocked down the officer while speeding in 2012.
The high-profile case has attracted criticism that the elite enjoy special treatment from Thai authorities.
Singapore airport authorities had confirmed with them that Vorayuth Yoovidhya’s private plane was in the country as of April 25, the AP reports.
Singapore does not have an extradition agreement with Thailand, but the two countries frequently co-operate in transnational cases.
Vorayuth Yoovidhya has repeatedly failed to meet Thai police to face charges of speeding, reckless driving causing death, and fleeing the scene of an accident. Some charges have since expired.
Red Bull heir’s representatives have said each time that he was either away for business or too ill to meet police.
Thai news outlets quoted police as saying that Vorayuth Yoovidhya traveled to Singapore on April 25, and that they were unable to stop him as this was before the warrant was issued on April 28.
A police spokesman also told The Nation newspaper that they did not put in place a travel ban as the case was about recklessness rather than one of criminal intent.
Thai investigators are now seeking to cancel Vorayuth Yoovidhya’s passport.
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