Over the course of the panel's 18-month investigation into Goldman, which has included two subpoenas, committee aides said they had obtained around 2 million documents. Asked if the panel had met with witnesses such as Tourre over the weekend, an aide would only say that they have met with a number of Goldman executives over the past few weeks.
Levin said Monday he would wait until after the hearing to decide whether to refer the panel's findings to the Justice Department and the SEC for possible criminal charges.
Today's showdown with Goldman Sachs comes just as Congress is considering the most sweeping new regulations for Wall Street since the Great Depression. This, the bill's proponents hope, will create an urgency to get financial overhaul through Congress.
"We've got to eliminate conflict of interest -- that really goes to the heart of the problem here -- is to whether you can be both selling securities to people at the same time you're betting against those securities," Levin said. "People really want reform here, they want to correct these abuses and I hope that Congress has the willpower and backbone to do it."
But experts are unsure whether legislation will actually change the way Wall Street firms operate.
"I predict that after the legislation is passed, Goldman will quietly, or not so quietly, find a way to settle. Whether they'll change the way they do their business, why do scorpions sting?" Cohan said. "I don't think that there's going to be much changing going on unless you really get at the incentives of what drives Wall Street's behavior."
ABC News' Huma Khan contributed to this report.