Swiss central bank chief Philipp Hildebrand is due to break his silence later on Thursday over his wife\'s controversial dollar purchase that has sparked a growing scandal and speculation over insider trading. Hildebrand, 48, will give a public statement at the Swiss National Bank in Zurich on the affair which has already seen two separate probes and a banking industry worker sacked. It emerged last month that his wife Kashya Hildebrand profited after buying $504,000 in August, just weeks before an intervention by the SNB to halt the rise of the franc -- a move that saw the dollar rise significantly against the Swiss currency. The purchase, which investigators said appeared to have been carried out without her husband\'s knowledge, was deemed \"sensitive\" by auditors who nevertheless cleared the couple of any wrongdoing. The report by PricewaterCoopers listed a number of other currency trades which on Thursday led one Swiss newspaper, the weekly Weltwoche, to dub him \"speculator Hildebrand.\" The affair has raised questions over current central banking regulations and ethics. The daily Berner Zeitung said Hildebrand should quit, saying the SNB needed to have \"absolute integrity,\" while the Basler Zeitung wrote that his stepping down was \"inevitable\". Le Temps said SNB regulations, including those regarding currency transactions, were \"clearly more lax\" than those of the European Central Bank and the US Federal Reserve. The Swiss government, whose own Federal Audit Office carried out a dual investigation exonerating the couple, is standing by the bank chief. \"The audit revealed no indication of any transactions in which inside knowledge of confidential facts had been used or which were contrary to the rules of the SNB,\" the Federal Council said in a statement. Hildebrand joined the SNB board in 2003 after a spell as chief investment officer at the Vontobel Group in Zurich and Union Bancaire Privee in Geneva. His appoint as chairman in January 2010 was largely well received by the media and commentators. Hildebrand\'s credentials also saw him selected as vice chairman of the Financial Stability Board last year and he is a member of the board of directors of the Bank for International Settlements (BIS) in Basel. The banker has yet to comment personally on the currency trading speculation but his wife, a former hedge fund worker who now runs an art gallery, defended herself earlier this week. In a written statement to the SF Swiss television, she said that she bought the dollars due to the fact that they had \"hit a very low level and become ridiculously cheap.\" The SNB on September 6 imposed a bottom limit for the franc against the euro to stop the currency soaring and biting into Swiss exporters\' earnings. The action saw both the euro and the dollar rise against the franc. The Hildebrands\' bank, Banque Sarasin in Basel, this week dismissed an employee who admitted illegally transmitting transaction details to a lawyer close to the far-right Swiss People\'s Party whose chief is a Hildebrand critic. Le Temps newspaper reported earlier this week that the party\'s figurehead Christoph Blocher went to then president Micheline Calmy-Rey with the extracts, sparking the affair. Blocher, a critic of SNB policy under Hildebrand, has so far remained silent on the affair.