Embattled lawyer Sittra Biabungkerd was quizzed on Wednesday by election officials for allegedly having run for the Senate despite being unqualified to seek the post.
Samut Sakhon provincial election officials visited Mr Sittra and questioned him at the Bangkok Remand Prison where he is being held on charges of fraud.
Phongphat Saichangthong, director of the provincial election office, said the office was ordered by the Election Commission to grill Mr Sittra following a complaint that the lawyer has failed to have engaged in social welfare work for at least 10 years, one of the criteria for standing as a candidate for the Senate.
Mr Sittra, a native of Krathum Baen district of Samut Sakhon, contested both the intra- and inter-professional rounds in the Senate polls between June 9-26.
He ran in Group 17, which was reserved for law practitioners and professionals in litigation and legal affairs.
The lawyer was not elected but he did place fourth in Group 17's reserve list.
Mr Phongphat said on Wednesday the election office decided to interview Mr Sittra at the prison because they had no idea when he would be released or available for questioning.
Mr Sittra has been quoted in media reports as saying he would not seek bail.
The election office has been given a deadline to question Mr Sittra. "And we can't keep delaying the process forever. It wouldn't be right," Mr Phongphat said.
He said the office made an appointment to question Mr Sittra once before he went to prison. However, the lawyer requested a postponement.
"The EC has told the provincial election office to gather additional information from Mr Sittra," Mr Phongphat said, adding Mr Sittra deserves a fair chance to give his side of the story.
However, an accused party is also entitled to refuse to speak to election officials and deny the allegation.
After the questioning is concluded, the office will wrap up its probe and send a report to the EC, which will meet to review the complaint and the investigation summary.
If the EC concludes Mr Sittra applied for a Senate seat knowing he was unqualified to run, he will have violated the Senate election law.
That is punishable by up to 10 years in jail and a fine of 20,000-200,000 baht.
He could also be banned from contesting elections for up to 20 years.