After four days on the stand, Ms Darinne Ko stepped down as a witness on Tuesday afternoon, in the sex-for-grades case.

Senior special investigator Png Chen Chen from the Corrupt Practices Investigation Bureau (CPIB) then took the stand. She told the court that she had been assigned to interview Ms Ko, a key witness in the trial. Ms Png said Ms Ko was calm and responsive from the time CPIB officers picked her up from her Bukit Timah home on April 2 2010, to the time that she reached the bureau.

During the journey, Ms Ko volunteered information about other students who were close to Tey and who had given him gifts too, said Ms Png. The names of some of these students have been highlighted during the past few days of court proceedings.

Ms Ko is said to have given gifts and sex to law professor Tey Tsun Hang. Tey faces six charges of corruptly obtaining these and giving Ms Ko good grades in return.