Law prof Tey questions CPIB officer in "trial within a trial" of corruption case

The law professor on trial for corruption in a sex-for-grades case is cross-examining an anti-graft officer on the admissibility of one of six statements - in what's called a "trial within a trial". 

Tey Tsun Hang is questioning Mr Bay Chun How to prove his case that the statement given to the Corrupt Practices Investigation Bureau (CPIB) was made under duress. 

If he can prove this, he'll able to argue that the evidence cannot be admitted in court. 

This would weaken the prosecution's case. 

Five other statements of Tey are being disputed. 

Two were recorded by CPIB officer Wilson Khoo and three by Deputy Director Teng Khee Fatt. 

They're expected to take the stand in the "trial within a trial".

Tey, 41, faces six allegations of obtaining gratification in the form of gifts and sex from his former student, Ms Darinne Ko, between May and July 2010, in exchange for lifting her grades.