The Federal Reserve gave just five banks the chance to bid on $6.2 billion in taxpayer-owned AIG assets before selling them to Goldman Sachs on Wednesday.

The Fed allowed Goldman Sachs, Barclays, Credit Suisse, the Royal Bank of Scotland, and Morgan Stanley to participate in the auction, according to a New York Fed statement. Reports of the auction leaked just days before the Federal Reserve announced the sale.

Some investors told Bloomberg News that the Fed's decision to keep the auction secret was unfair to both investors and taxpayers. They said that if the bank had allowed the free market to set the price for the assets, the sale would have earned taxpayers more money.

"The exclusivity by which the process has shut out smaller dealers is a little un-American.... It seems odd that if you want to get the best possible price that it wouldn't be open to anyone who wants to put in the most competitive bid," David Castillo, head of sales and trading at Further Lane Securities, told Bloomberg News.

New York Fed spokesperson Andrea Priest wrote in a statement that the sales process was competitive and realized an "excellent value for taxpayers." This sale "will enable full repayment" of a loan from the New York Fed to the group of AIG securities, she wrote.

"We did not simply accept an offer to buy a bundle of securities - we forced the bidder to compete with other potential buyers," Priest wrote. "The participants were selected using objective criteria based on how active they are in this market."

The New York Fed's statement on Wednesday noted that the auction was prompted by an unsolicited offer by Credit Suisse to buy the securities. It did not specify the amount of Goldman's winning bid. Just two out of 24 sales of the AIG securities have been closed, according to Bloomberg News.

The New York Fed held open auctions for individual AIG bonds last spring but didn't get the highest possible prices, as investors fretted about the crisis in Europe and the markets fell, according to the WSJ.

The bonds are part of a package called Maiden Lane II, which absorbed AIG's toxic mortgage-backed securities in order to help prevent AIG's collapse during the financial crisis.

The Federal Reserve sold $7.01 billion in Maiden Lane II securities to Credit Suisse on January 19 in a similarly closed auction. The Fed invited just Goldman Sachs, Credit Suisse, Barclays, and Merrill Lynch to participate, according to its statement. Goldman Sachs had approached the New York Fed in January offering to buy those securities, according to Bloomberg News.

These two sales whittle down the total amount left in the Maiden Lane II portfolio to $6.2 billion.