A former investigator for an independent inquiry into the UN oil-for-food programme handed over potentially explosive documents on Thursday to a US congressional committee, triggering outrage from inquiry head Paul Volcker. Robert Parton, a lawyer and former FBI agent who resigned last month as senior investigative counsel for the inquiry, gave the documents to US lawmakers even though he signed a confidentiality agreement when he was hired and certified when he left that he possessed no documents related to his work. Congressional investigators speculate the documents could show that UN Secretary-General Kofi Annan misled Volcker, a former chairman of the US Federal Reserve Board, during the investigation. Annan has repeatedly insisted he committed no wrongdoing, was truthful and withheld nothing from investigators. Parton has told associates he felt Volcker's inquiry had been too soft on Annan when it looked into whether the UN chief interfered in the awarding of a lucrative contract in Iraq to the Swiss firm Cotecna, which employed his son Kojo.