Andrew Cuomo, New York attorney general, has issued subpoenas to one current and four former board members of Bank of America, insisting they testify under oath about what they knew in the months leading to BoA’s controversial acquisition of Merrill Lynch, the Financial Times reported.

Mr Cuomo will eventually call all 15 outside members of last year’s BoA board, nine of whom have since left, the newspaper said, quoting an unnamed source. Mr Cuomo is trying to determine whether Ken Lewis, BoA chief executive, kept board members apprised of mounting losses at Merrill and Merrill’s plans to pay out $3.6 billion in bonuses on an accelerated basis.

The purchase of Merrill Lynch created the world’s biggest wealth management firm and happened just months after the banking world was rocked by the bankruptcy of Lehman Brothers and huge losses at firms such as Citigroup, Merrill, AIG and UBS.

Earlier this week, a US federal court dismissed a deal between Bank of America and the Securities and Exchange Commission that would have settled the SEC's complaint that the BoA misled shareholders about its plans to pay Merrill Lynch executives bonuses for 2008.

Until now, Mr Cuomo’s investigation has focused on whether executives violated disclosure laws leading up to the 5 December shareholder vote that ultimately approved the merger.

The first five board members to be subpoenaed, according to the source, are: William Barnet, John Collins, Tommy Franks, Thomas May and Joseph Prueher.

Mr May continues as chairman of Bank of America’s audit committee, but the other four left this year.

Mr Cuomo has been investigating BoA’s management since January, after it was reported that Merrill had accelerated payments of $3.6 billion bonuses in a year in which Merrill lost $28 billion and BoA needed $20 billion in taxpayer funds to complete its acquisition.