Reports that Credit Suisse (CS) and BNP Paribas  (BNPQY) may be hit with criminal charges stunned Wall Street Wednesday as it potentially marks a dramatic shift in how Federal prosecutors look at the financial services industry.

Since the 2008 crisis and up to and including JPMorgan's (JPM) settlement for enabling Bernie Madoff earlier this year, U.S. regulators have typically sought to settle cases of alleged misdeeds rather than pursue criminal charges. Typically, the big banks pay a fine without having to admit to any wrongdoing and no senior executives have suffered anything more than, perhaps, deferred bonuses.

In his latest book, The Divide, Matt Taibbi set out to examine why Wall Street has been largely immune from prosecution since the 2008 crisis; that's in contrast to the S&L crisis of the 1980s -- when over 800 bankers went to jail -- and the accounting scandals of the early 2000s, when high profile CEOs like Enron's Jeffrey Skilling, WorldCom's Bernie Ebbers, Tyco's Dennis Kozlowski and Adelphia's John Rigas went to jail for various crimes.

"After 2008 - certainly there were no less ethical misdeeds -- but we've seen nothing, not even symbolic prosecutions," Taibbi says. "It's qualitatively different."

Related: How income inequality can lead to more financial crises

Taibbi, who recently left Rolling Stone for Pierre Omidyar's First Look Media, is highly critical of the Obama Administration for failing to prosecute Wall Street crimes. But he concedes the change in how federal prosecutors view Wall Street predates Obama's rise and stems from a variety of factors, including:

• The Democrats embrace of the financial services industry in the 1990's under President Clinton, which, over time, evolved "from deregulation to non-enforcement."

• A 1999 memo by (then) deputy U.S. Attorney General Eric Holder which warned of "collateral consequences" of prosecuting corporate crimes.

• The fallout from the 2002 "death sentence" of Arthur Andersen, which was later overturned by the Supreme Court -- embarrassing the Justice Department -- but came far too late to save the firm or the jobs lost when it lost its accounting license. ('Collateral consequences', indeed.)

• An influx of corporate lawyers into the Justice Department, which Taibbi says "resulted in more settlements as opposed to a perp walk, which is the old way of doing things."

These developments, plus fear of "systemic risk" if a big bank were to be criminally prosecuted, have conspired to where (now) U.S. Attorney General Holder recently expressed concern “that the size of some of these institutions becomes so large that it does become difficult for us to prosecute them.”