Prosecutor Billy Downer could be forced into the dock and potentially disqualified from leading the corruption case against Jacob Zuma if the state is stopped from obtaining original evidence from Mauritius.

State counsel Wim Trengove SC argued in the Constitutional Court yesterday that Downer's cross-examination by Zuma's legal team was one of the scenarios that could follow if the National Prosecuting Authority (NPA) was barred from requesting 14 documents, used to convict Zuma's former financial adviser Schabir Shaik of fraud, from Mauritian authorities.

Cross-examination of any such witnesses involved in obtaining the documents most prominent of whom would be Downer could then be used as a means of undermining the state advocate's objectivity.

While Zuma's counsel, Kemp J Kemp SC, this week shied away from naming Downer as a possible target, he confirmed that the ANC president wanted the right to cross-examine witnesses.

In response to questions by Justice Kate O'Regan, Kemp explained the motivation behind Zuma's desire to cross-examine witnesses connected to the documents.

"We contend that the copies were brought here in an improper way, that the NDPP (National Directorate of Public Prosecutions) got its hands on them in an impermissible manner. We have a fair idea of what went on, but we can't present that to the court.

"If the state does not call witnesses, we cannot cross-examine them."

Kemp added: "We say that the state wishes to avoid a situation where witnesses are called.

"We want them to call witnesses. We want to preserve and exercise the right to challenge the evidence."

Downer has come under repeated attack from Zuma and his corruption co-accused, French arms company Thint, over the allegedly unlawful way he obtained the copies of the documents.

In documents before the Durban High Court, Zuma's legal team contended that the state was attempting to avoid "cross-examination in Mauritius of witnesses which will expose exactly what occurred during the first search and seizure and its aftermath which will impact not only on the procurement of the copies, but also the originals and even cast a pall over the Shaik proceedings".

Thint CEO Pierre Moynot, in an affidavit recently filed before the Mauritian Supreme Court, has claimed Mauritian authorities authorised only the search and seizure of the documents and not their copying and handing over to Downer.

"I believe that the possession of the documents by the South African authorities is unlawful," he said, alleging that the usual diplomatic channels were not followed.

Moynot claimed that initial requests in 2001 by the NPA were denied by the high commission of Mauritius in Pretoria.

"It was only after the intervention of Mr Downer (which we believe was not authorised) that the ex parte application was brought in the Supreme Court of Mauritius on October 5 2001," he said.

The state is expected to respond to Moynot's claims later this month, but has previously rubbished any suggestion that Downer acted improperly.

Moynot yesterday sat alone in the court's front row, after Zuma elected not to attend the final day of his marathon court bid to challenge warrants used to search-and-seize his and Thint's homes and offices, as well as the state's request to the Mauritian authorities.

Constitutional Court Chief Justice Pius Langa has reserved judgment on both applications.

With acknowledgements to Karyn Maughan, Tania Broughton and The Star.