Deputy police spokesman Colonel Krisana Patthanacharoen reported Jenpop’s pleas, citing the defendant’s lawyer. Krisana also said that test results to determine whether Jenpop, 37, had been driving under the influence of drugs would be available today.

The investigators’ initial report indicated that Jenpop might have been driving while under the influence, contributing to the accident that killed postgraduate students Thantapat Horsaengchai and Krissana Thaworn.

The Phra In Racha police superintendent has been transferred from his post for 15 days to allow newly assigned investigators to take over the case, Krisana said, adding that police would investigate and prosecute any culprit involved.

Addressing rumours that Jenpop may have a bipolar disorder that had a bearing on the case, Krisana said he could not confirm that or give details about medication found in the suspect’s car until there had been a doctor’s examination.

Attorney-General Pol Sub-Lieutenant Pongniwat Yuthaphanboriparn said he would assign the chief officer of the Regional Office of State Attorney Region 1 to take charge of the case after police handed it off to his office.

Pongniwat added that progress in another case, in which Red Bull heir Vorayuth Yoovidhya is accused of killing Pol Snr Sgt-Major Wichean Klinprasert in a hit-and-run accident in September 2012, was ongoing and that prosecutors required police to investigate to clarity certain points.

A source said Vorayuth initially had faced three charges of reckless driving resulting in death and property damage, failing to stop and aid a victim, and speeding. The last charge has been dropped because the statute of limitations expired in 2013.