It is important that the National Prosecuting Authority (NPA) should act, and be seen to act, independently of political fear or favour. That's why the shenanigans surrounding the NPA's Scorpions investigation into deputy president Jacob Zuma's alleged involvement in arms deal corruption must be exposed for the dirt that it is, and stopped.

We must root out corruption in state contracts. Mind games only detract from that, which may be one reason they have crept into this most politicised of corruption cases.

As we report this week there is reason to believe that the Scorpions' written questions to Zuma were leaked to the press not by the Scorpions but by a third party. It is possible that, in an effort to discredit the investigation, it was leaked by someone close to Zuma, since he and his lawyer were the only party, outside of the Scorpions, who had the version of the questions that was handed to the Sunday Times. According to the Scorpions, only national director of prosecutions Bulelani Ngcuka and the unit's head, Leonard McCarthy, had it. And why would they want to bring suspicion and disgrace on their office by leaking it?

The leak fits the context of a months-long rumour campaign against Ngcuka's personal and professional integrity. He himself has accused unnamed "comrade criminals" of being behind the smear. But such a response oozes political innuendo unbecoming of SA's most senior prosecutor. His view, expressed to City Press last week, that past sentences on Winnie Madikizela-Mandela and Tony Yengeni were "excessive", is also out of place.

There was a concern about political bias when the NPA was created under constitutional mandate in 1998. Critics felt that centralising the prosecution service risked executive interference. What made this of more than theoretical concern is the fact that the NPA has teeth - it combines investigative and prosecutorial functions, a subject of controversy.

Over the past five years the NPA has allayed most of these fears because it has succeeded in raising the morale and efficiency of prosecutors, and because the Scorpions and Asset Forfeiture Unit have made notable headway against crime.

Ngcuka and his cohorts should build on that success. There is too much at stake to ruin that hard-won credibility by engaging in mere politics that dilute its core competencies.

 With acknowledgement to the Financial Mail.