The investigating panel invited Vicha Mahakun, head of an inquiry into the Boss case, and Khemchai Chutiwong, former deputy attorney general, to testify.
However, the legal procedure has been halted after Nate filed a letter to oppose the investigation, complaining that he was not informed of the interrogation in advance.
The Public Prosecutor Commission said it will consider Nate’s objection on November 30. Meanwhile the testimony of Vicha and Khemchai has been delayed.
Nate’s decision in June to drop the final charge against Vorayuth, heir to one of Thailand’s richest families, sparked public outrage and several official inquiries into the case.
The case resumed in September with Vorayuth indicted on two charges, of reckless driving causing death, and cocaine use. Vorayuth is accused of crashing his car into police officer Wichian Klanprasert in 2012, killing him.