One of the two witnesses in the Red Bull scion Vorayuth "Boss" Yoovidhya case died following a motorcycle accident in Chiang Mai province in the early hours of Thursday.

Jaruchart Maadthong, 40, was involved in a motorcycle accident at 1am. He died shortly after at Maharaj Nakorn Chiang Mai Hospital.

His body was sent for an autopsy. His family and relatives said they knew nothing about his involvement in the high-profile case.

The Chiang Rai native was one of two new key witnesses added to the case two years ago. The other was a retired officer, Air Marshal Jakkrit Thanomkulabutr. Both testified that the Ferrari was travelling at 50-60 km/hour when the crash occurred.    

The two witnesses also testified that they saw a policeman on a motorcycle abruptly cut in front of Mr Vorayuth’s Ferrari, causing him to hit the bike. As a result, the dead policeman was named another suspect in the case alongside Mr Vorayuth.

Both were due to meet the House panel on justice and Aug 5. The chairman of the panel urged the police chief to give protection to the air marshal as he was the only remaining key to a trial. 

Deputy attorney-general Nate Naksook, on behalf of the attorney-general, signed the order not to charge Mr Vorayuth in late June but Thai media did not know about it until CNN broke the news last week.