National Director of Public Prosecutions Bulelani Ngcuka has accused senior government and ANC figures being investigated by the Scorpions of waging a vicious campaign to discredit him and his department.

"There has been a systematic disinformation campaign to discredit me and my organisation by those whom we are investigating, thereby diverting the public attention from their criminal conduct.

"We have acted without fear, favour or prejudice in defence of democracy," said Ngcuka in an address to the annual dinner of the Foreign Correspondents' Association in Johannesburg at the weekend.

While he did not name Deputy President Jacob Zuma or ANC veteran Mac Maharaj, he left little doubt his remarks were directed at them and others - like Zuma's financial adviser Schabir Shaik - under investigation by the Scorpions in their probe of corruption in the multibillion-rand arms deal.

"Their strategy was simple: 'throw as much dirt on them as you can, and hope some of it sticks'. But this has failed and will continue to fail, for it does not matter how deep the truth may be buried, it is never destroyed."

Ngcuka hit out at his critics within the ruling ANC and said he would be vindicated by his statement that there was prima facie evidence of corruption against Zuma when Shaik's trial got under way.

"Evidence against the deputy president will come out in the trial of Shaik," he said in response to a question. When you were dealing with a head of state or deputy president, you could not afford to lay charges unless you were assured of success, he added.

He said his team in the Scorpions had decided they should prosecute. "They said there was a case for prosecution.

"I found some shortcomings and they agreed, which meant there was insufficient evidence to guarantee we could get a conviction."

He said it would have been wrong to lie to the public and would have compromised the institution if he had done so.

He said that although the Scorpions had had many successes in most high-profile cases, it was the investigation into the arms deal that had marked the biggest test for democracy in South Africa.

"The decision to investigate the deputy president was not an easy one," Ngcuka said.

"I believe it is because of the commitment to our ideals and support for the safeguarding and protection of our democracy that the National Prosecuting Authority finds itself under attack."

He said the NPA had been able to conduct the investigation and take the decisions without any political interference or interventions.

Ngcuka praised the conduct of the media overall but said some journalists had abused their positions.

"The manner in which a number of issues relating to the arms investigation were handled, and the conduct of certain journalists and editors, highlight the dangers of abusing press freedom and journalistic privilege in a way that can shake the very foundations of our democracy and undermine the rule of law."

With acknowledgements to John Battersby and The Star.