June 12 (Bloomberg) -- U.S. taxpayers have reaped a 7.5 percent return on the $45 billion used to rescue Citigroup Inc., more than three times as much as if the money had been invested in the Standard & Poorâs 500 Index. Chief Executive Officer Vikram Pandit, summoned by Congress in February to explain his bankâs use of the funds, vowed to âmake this a profitable investment for the American people.â The return since the government first purchased a stake in the bank on Oct. 28, which includes dividends, compares with 2.4 percent for the S&P 500 through yesterday on that basis. http://www.bloomberg.com/apps/news?pid=20601109&sid=apay4rDTGMTw