Without Durban businessman Schabir Shaik answering their questions – even with an innocent explanation – the Scorpions will not be able to complete their probe of the arms deal.

The investigation leader, advocate Billy Downer, further stated in an affidavit filed at the Constitutional Court yesterday that Shaik "is the only witness available to the investigation, and his participation is crucial".

But of course the Scorpions are no longer interested in asking Shaik any questions around a conference table, but will see him in the dock next year when his trial on charges of tax evasion, corruption and fraud relating to the arms deal, and his position as Deputy President Jacob Zuma's financial adviser, gets under way in the Durban High Court.

Shaik's legal team fired back in their papers filed at the Constitutional Court, saying there was no evidence to show why the Scorpions, with their wide-ranging powers of investigation (which are open to abuse), should have probed the arms deal, because the police could have done it.

"The integrity of the legal system is less likely to be damaged by a questioning (in the Scorpions' way) than it is by the failure to root out corruption," counsel for the National Prosecuting Authority (NPA), Marumo Moerane SC, replied in his heads of argument.

Shaik took on Justice Minister Penuell Maduna, National Director of Public Prosecutions Bulelani Ngcuka, Scorpions chief Leonard McCarthy, as well as arms deal investigators Downer and advocate Gerda Ferreira in the Constitutional Court.

He wants part of the National Prosecuting Authority Act, which allows investigators to question people involved in suspected crimes, to be declared unconstitutional.

He earlier lost a similar case in the Durban High Court, where Judge Ron McLaren said it was not unconstitutional.

The NPA argues that if it questions a person without any charges pending, that person does not have the right to be protected against giving self-incriminating evidence, because he or she has not yet been arrested.

While the Constitutional Court appeal was still pending, Shaik was charged with fraud, tax evasion and corruption.

His lawyers say the matter has been brought before the Constitutional Court in the interest of justice. The legal team for the NPA says that apart from this, it is only of academic value because Shaik is now an accused and not a suspect.

Shaik's legal team, however, says that at the time the Scorpions wanted to ask him questions, Downer "believed … the evidence revealed that Shaik, Deputy President Jacob Zuma and French arms dealer Alain Thetard all conspired to elicit a bribe in exchange for political favours … (and) in support of this theory, the Scorpions apparently also obtained evidence from witnesses and documentary evidence".

They continue in papers before the court: "Evidently, something happened between the hearing … (when a certificate giving them leave to appeal to the Constitutional Court was given) on August 12 2003 and service of these papers on the state attorney on August 22 2003.

"Whatever occurred, the inference is irresistible that, contrary to the basis on which the Scorpions, Ngcuka and Maduna dealt with the matter, sufficient evidence was available and had always been available on which to decide whether to prosecute Shaik."

Corruption is not an "ordinary" crime, the Scorpions' legal team said in papers before the court.

The Constitutional Court yesterday reserved judgment in Shaik's application for leave to appeal against the Durban High Court ruling, Sapa reports.

With acknowledgements to Estelle Ellis and The Star.