The decision to drop the case against Jacob Zuma because of spy tapes suggesting political meddling has failed to clear the name of the country's likely next President, commentators said on Monday.

"The whole question of whether Zuma is guilty is as unsettled as before and will never be settled," political analyst Steven Friedman said.

"It is not good for our system, it is not a healthy situation. I'm not saying he's guilty, but he at the very least ought to be aware that he has a credibility problem and needs to address that problem."

Constitutional law expert Shadrack Gutto agreed, saying since the National Prosecuting Authority (NPA) stated clearly on Monday that it had been given no reason to change its mind about the merit of its corruption, fraud, racketeering and money laundering case against Zuma, suspicions remained.

"The NPA indicated very clearly from the outset, that on merit nothing could make them change their mind, which means there is still a very strong case against Jacob Zuma."

Gutto said the NPA had acted within its rights to decide not to prosecute, but questioned whether the body had not bowed to political pressure, including a sustained propaganda campaign, to scrap the case against Zuma.

"The NPA has a right to decide to prosecute or not to prosecute but the Constitution also says it has to be done without fear, favour or prejudice.

"The question is, whether there was any pressure and indeed we have for weeks been bombarded with information, through certain leaks to the media, indicating that the charges would be dropped before there was any decision.

"From that point of view, we can question whether this is not tantamount to political pressure."

Constitutional law expert Pierre de Vos said he believed the NPA was "on very thin ice" in its reasons for scrapping the case.

Acting NPA boss Mokotedi Mpshe concluded it was not possible to proceed because former Scorpions head Leonard McCarthy appeared in taped phone conversations to take political orders on the strategic timing of proceeding against Zuma.

Mpshe read transcripts to the media on Monday in which former NPA head Bulelani Ngcuka urged McCarthy to act before the African National Congress (ANC) conference in Polokwane in 2007, where Zuma's power struggle with then-President Thabo Mbeki came to a head.

Said De Vos: "One is not sure whether that is a legal argument. It is very problematic. They should have left it for a court to decide.

"Instead of clearing its name, the NPA has further muddied the waters. The decision was not a wise one. I agree with the lawyers and not the political bosses of the NPA."

Friedman argued that the case for interference was not clear cut as undertakings given by McCarthy never transpired.

"I'm not sure... that McCarthy succeeded in influencing the case. If you look at the transcripts, you cannot make a case that
McCarthy so poisoned the case that it could not proceed."

Other legal experts studying the case said McCarthy and Ngcuka could claim that they had been defamed but said the NPA could counter that it was in the public interest to reveal the content of the phone recordings.