On the eve of a crucial deadline today for Deputy President Jacob Zuma to answer questions on allegations that he solicited a bribe, the Scorpions investigator heading the investigation, Gerda Ferreira, has resigned.

While the Scorpions insist there is nothing sinister in her resignation and that it would not derail the Zuma probe, Ferreira's departure is being seen as a setback for the investigation, particularly following her successful prosecution of disgraced former African National Congress parliamentary chief whip Tony Yengeni for lying to Parliament.

Scorpions spokesman Sipho Ngwema said Ferreira had received an excellent offer from a financial institution some time ago. The organisation had come to an arrangement that she would continue to assist with the case.

"Government can't match private sector salaries and although Gerda will always be a prosecutor, she is only human and has financial obligations too."

Ngwema said the decision was painful for all concerned and that Ferreira would "always belong to this organisation".

Meanwhile, opposition parties have questioned the motives behind remarks by President Thabo Mbeki on the future location of the Scorpions.

Democratic Alliance (DA) chief whip Douglas Gibson said it was never a good idea to have both the police and the Scorpions operating within the country's borders.

This was especially so if one of these agencies the Scorpions reported directly to the president, Gibson said.

"But one must wonder why the president has suddenly now decided to agree with the DA's position of five years ago," he said. "It is ominous that just when the Scorpions have proved that they can sting, the president now proposes moving them. If any such move takes place, it needs to be properly debated in Parliament and the investigation against the deputy president and any other politicians or officials involved in the arms deal finally completed."

United Democratic Movement leader Bantu Holomisa also expressed concern about the timing of Mbeki's remarks. "The Scorpions are a creation of his (Mbeki's) administration and there can be no confusion about whom they report to and why."

"President Mbeki is after all part of the Cabinet that took the decision to create the Scorpions. Why the sudden confusion about the Scorpions?" he asked.

"When the Scorpions, along with other agencies, exonerated government of wrongdoing in the arms deal, no questions were raised about their functioning.

"To suddenly raise this issue now, when the Scorpions are finally investigating the role of high-ranking government and African National Congress officials in the arms deal, reeks of expedient concern for what they may expose," he said.

With acknowledgements to Wyndham Hartley, Tim Cohen and the Business Day.