The National Intelligence Agency (NIA) could be guilty of an offence much more serious than that of those heard to be conspiring on the tapes released by National Prosecuting Authority (NPA) boss Mokotedi Mpshe, prominent constitutional law expert advocate Wim Trengove, SC, said yesterday.

Speaking at a public seminar at the University of Cape Town, Trengrove said the question of the NIA's conduct was still unresolved.

The release of secret evidence to save ANC president Jacob Zuma could amount to gross misconduct much more serious than those heard to be conspiring on the spy-tapes, he said, and may "on the face of it" have infringed three different laws guiding the secret services.

He said South Africa could not tolerate the "kind of lawless state" in which intelligence agencies could get away with releasing evidence to "a rising political star" and for him to use it for his own political purposes.

"It is critical (to know) because they are so powerful and they operate in secret and we need to trust them, Trengove said. "And to find that they have released masses of information to a politician for his personal use, without (there being) justification, seems to me to be criminal."

He said Zuma's legal team also needed to "come clean" on how the recordings came into their possession, because on the face of it, there seemed to be a crime of illicitly receiving and using the information for personal gain.

"On the face of it, Zuma's team received these tapes illicitly from NIA and kept and used it for his personal benefit," Trengove said. "I don't know how (they got it). But it seems illegal."

Trengrove said Mpshe's decision to stay charges against Zuma was unlawful and a tipping point on a "slippery slope" for the rule of law.

Mpshe had not sufficiently weighed up the public interest in seeing justice done, particularly regarding those alleged to have abused public office.

Trengove said Mpshe's decision was based largely on peripheral considerations such as "eleventh-hour shenanigans relating to the timing of the prosecution".

The saga had also sent "ominous" signals that the very fabric of society and the Constitution could be eroded. He appealed to civil society and to lawyers to take a stand.

Trengove has represented the NPA several times in opposing Zuma's legal bids to have his prosecution on corruption and other charges stayed.

He said the decision was unlawful because it would not stand the test of reasonableness when taking into account the public interest in ensuring that a public figure stands trial for an offence. Mpshe had failed to apply the two-step test he had set himself, which would have required him to not only establish whether the case was fatally infected by manipulation - as indicated by taped discussions between former prosecutions boss Bulelani Ngcuka and ex-Scorpions chief Leonard McCarthy - but also whether this contamination outweighed the public interest in seeing justice done.

"It seems to me Mpshe never asked this question," said Trengove.

"He never tried to balance the offensive conduct on the one hand, limited to a timing decision as it was, with the countervailing public interest, the one that outrages us so. And that is ensuring that all people are treated equally - that those who are charged with grave crimes should stand trial, whether in high office or not."

Calling the decision "inexplicable", Trengove said Mpshe's conduct "seems to be that of one only too relieved to find an escape from unbearable pressures".