The New York attorney general Eliot Spitzer spread his investigative web this week to put together "powerful and substantial" evidence of misleading practices at AIG.

The evidence was met with silence from AIG former chairman Maurice 'Hank' Greenberg, who invoked his right to silence and refused to answer questions.

Warren Buffett, however, had no problems in coming forward to answer questions about Berkshire Hathaway's relationship with AIG.

Spitzer made clear that Buffett was not under suspicion, but acting as a witness in the case.

The investigations also widened this week with Munich Re being called in to talk to US regulators about its relationship with AIG.

Meanwhile, Willis has agreed to a $50m settlement fund with the New York attorney general to pay back clients who were unfairly charged contingent commissions.