The prosecution has not, even with its best case, made out the charges against former anti-narcotics bureau chief Ng Boon Gay, said defence lawyer Tan Chee Meng.

In his closing arguments today, Mr Tan sought to show why Ng should be acquitted of all four charges of corruption because the prosecution had not proven its case beyond a reasonable doubt.

Mr Tan argued that Ng did not influence the agency's IT procurement process and the procurement for two projects - NCD and Jardine - were all properly complied with. He also said that the prosecution's key witness, Ms Cecilia Sue, never asked for or expected any favours from his client, nor had Ng ever promised her any favours.

Mr Tan told the court that evidence actually shows that there was no compromise of Ng's duties even when the opportunity arose and he had in fact left IT matters to the bureau's IT department.

Ng, 46, is facing four charges of having corruptly obtained oral sex from former IT executive Ms Sue, 36, on four occasions in 2011. This is said to be in exchange for furthering the business interests of her then employers.

Ng, he said had kept an "arm's length" from the procurement processes and could have not thrown in a "spanner, screwdriver, hammer" into the works as far as Ms Sue's potential dealings with the CNB were concerned.

Mr Tan closing submission, which started at 9.35am today, will continue for about two hours, after which Deputy Public Prosecutor Tan Ken Hwee will have his turn during the day's hearing. The case will wraps up today after 14 days of testimony by 10 witnesses previously.

After that, it will be up to District Judge Siva Shanmugam to decide whether or not Ng is guilty. Ng, had arrived earlier for the hearings with his wife Low Yen Yen and a few family members. The verdict for the case is expected at a later date.