Just when you thought Wall Street couldn't sink any lower - when its excesses are still causing hardship to millions of Americans and its myriad abuses of public trust have already spread a miasma of cynicism over the entire economic system - an even deeper level of public-be-damned greed and corruption is revealed. Libor is the benchmark for trillions of dollars of loans worldwide - mortgage loans, small-business loans, personal loans. It's compiled by averaging the rates at which the major banks say they borrow. So far, the scandal has been limited to Barclays, a big, London bank that just paid $453 million to U.S. and British bank regulators, whose top executives have been forced to resign, and whose traders' e-mails give a chilling picture of how easily they got their colleagues to rig interest rates in order to make big bucks. But Wall Street has almost surely been involved in the same practice, including the usual suspects - JPMorgan Chase, Citigroup and Bank of America - because every major bank participates in setting the Libor rate, and Barclays couldn't have rigged it without their witting involvement. In fact, Barclays' defense has been that every major bank was fixing Libor in the same way, and for the same reason. And Barclays is cooperating" (i.e., providing damning evidence about other big banks) with the Justice Department and other regulators in order to avoid steeper penalties or criminal prosecutions, so the fireworks have just begun.