Virtually all independent economists and financial experts say that rampant fraud was largely responsible for the financial crisis. See this and this.
Similarly, leading economist Anna Schwartz - co-author of the leading book on the Great Depression with Milton Friedman - told the Wall Street journal in 2008:
I think we ought to go do what we did in the S&L [crisis] and actually put many of these guys in prison. Absolutely. These are not just white-collar crimes or little accidents. There were victims. That's the point. There were victims all over the world.
Economists focus on the whole notion of incentives. People have an incentive sometimes to behave badly, because they can make more money if they can cheat. If our economic system is going to work then we have to make sure that what they gain when they cheat is offset by a system of penalties.
As long as we keep up this strategy, it's going to be a long time before the economy recovers ....
It was four years after the crash of 1929 before the major titans of Wall Street were forced to give testimony under oath to Congress and the full magnitude of the fraud emerged. That delay may well have contributed to the depth and duration of the Great Depression. The modern-day Wall Street corruption hearings in Congress ... must now resume in earnest and with sworn testimony if we are to escape a similar fate.