The US Federal Reserve knew about Libor rigging three years before the financial scandal exploded but did not take any firm action, documents have revealed. According to newly published transcripts of the central bank's meetings in the run-up to and immediate aftermath of the collapse of Lehman Brothers, a senior Fed official first flagged the issue at a policy meeting in April 2008. William Dudley expressed fears that banks were being dishonest in the way they were calculating the London interbank offered rate - a global benchmark interest rate used as the basis for trillions of pounds of loans and financial contracts. Three years after his remarks, it emerged that traders at more than a dozen banks, including Lloyds, Royal Bank of Scotland and Barclays, had routinely been trying to fix the official Libor rate in order to boost their own bonuses and profits. The transcript of the Fed's April 2008 meeting raises questions about why the central bank did not move to properly tackle the scandal. There was no official regulator for Libor at the time, and officials at the US Federal Reserve tried to blame British authorities for allowing the benchmark interest rate to get out of control in the first place. The Fed declined to comment on the transcripts or why it had not taken firm action..