For a man of his background, it is unlikely that law professor Tey Tsun Hang would have failed to lodge an official complaint against the Corrupt Practices Investigation Bureau (CPIB) for alleged abuses he suffered while under questioning.

Chief District Judge Tan Siong Thye said this on Monday afternoon when the court received submissions from both the prosecution and defence of the ongoing trial within a trial. The mini-trial is set to determine if Tey, suspended from the law faculty at NUS since he was charged last July, had voluntarily given six statements to the CPIB. If he did so under threats, inducements and promises, the statements cannot be used as evidence in court.

"We have a situation where he (Tey) is a professor of law, was a former district judge, a former JLC (Justice of the Law clerk) former practitioner, and other than 2nd April, each time he returned to CPIB was on his own, he wasn't taken in," said Judge Tan.

The 41-year-old is accused of corruptly obtaining gifts and sex with an ex-student in exchange for better grades.

Yet, the judge said that Tey, in "voluntarily" returning to CPIB time and again, was like a man who had burnt his finger but continued to put it over a fire.

"It is natural instinct that if you were subjected to such harsh treatment, why would you voluntarily go back to the same trauma?" asked judge Tan.

Tey appeared to be uninterested throughout Monday's proceedings, and could be seen reading a small paperback on philosophy through most of the afternoon. This was a far cry from last week, when he strenuously defended himself and even broke down and cried once while on the stand.

CDJ Tan will on Tuesday issue his verdict on whether the six statements will be admissible as evidence, and the main trial will then continue.