NEW YORK (MarketWatch) — It’s the lingering question about the financial crisis: Why are no top executives of major Wall Street banks in jail more than three years after Lehman Brothers collapsed? Why have none even been charged with crimes?

Surely, someone must be guilty of something. Enron and the corporate scandals of the 2000s and the savings & loan failures of the early 1990s each resulted in more than 1,000 criminal convictions.

Jon Corzine testifies to Congress

But this time is different and I wanted to find out why. So I spoke with several federal prosecutors from the S&L and Enron eras, the people who actually brought successful criminal white-collar cases.

They told me it boils down to proving criminal intent beyond a reasonable doubt, resources and commitment.

Let’s start with the first point, which was made on “60 Minutes” last week and in the Wall Street Journal, where a former FBI official, David Cardona, said the Justice Department had decided to let regulators “take civil-enforcement actions”— like, say, the SEC’s actions against Citigroup, which Judge Jed S. Rakoff threw out last week — rather than go for criminal prosecutions, which have a much higher burden of proof.

Read Howard Gold’s piece on why the SEC needs to do more to take on big Wall Street firms in MoneyShow.com.

Samuel Buell, a professor at Duke University School of Law who was a lead prosecutor on the Department of Justice’s Enron Task Force from 2002 to 2004, told me the challenge in these cases is “coming up with strong evidence of criminal mental states.”

In other words, “you knew that you were putting out [material] that was false and misleading and you did it anyway,” he said.

Clear victims with Enron

That was what the government did with Enron top executives Kenneth Lay (who died after being convicted), Jeffrey Skilling (who is appealing his conviction), and Andrew Fastow (who co-operated with the government, pled guilty and served time).

Enron’s finances were in some ways as complex and sophisticated as the derivatives trades made by the big banks, and the consequences were huge.

“Everybody recognized at the time that this was a cataclysmic event for the financial system. We had never seen a Fortune 10 company blow up overnight,” Buell explained.

But at Enron, there were blatant misstatements by top executives who clearly knew things were worse than they said they were.

There were also clear victims — investors and employees who lost their life savings in the company’s 401(k) plan. “In any fraud case you need a victim,” said Buell. “In Enron, you could tell a story of mom-and-pop investors who were deceived.”

During that time, CEOs of companies like WorldCom and Adelphia Communications also were convicted and sentenced to long prison terms.

But in the financial crisis, the questionable transactions were conducted by big banks with other large institutions whose executives presumably should have known what they were buying — and even that the banks might short the very instruments they were purchasing. The rest of us were just collateral damage.

Read Howard Gold’s piece explaining Goldman Sachs’ many conflicts of interest on MoneyShow.com.

Making the connections

Linking top executives to specific instances of fraud is a big problem, says Joshua Hochberg, who ran the Department of Justice’s fraud section during Enron and is now a partner at McKenna Long & Aldridge in Washington. “How do you tie them to the actual fraudulent mortgages or sale of products they knew were bad?” he asked. (Obviously that could be different for the mortgage originators themselves, like Countrywide, if the allegations in the “60 Minutes” piece were correct.)

That wasn’t a problem with the savings & loans. “The thrift savings cases largely involved people [profiting] directly from the loans they were authorizing,” said Hochberg.

Back in the late 1980s, I covered CenTrust Bank in Miami, whose chairman David L. Paul sailed a 95-foot yacht and, allegedly with bank money, purchased an old-master painting by Peter Paul Rubens which he displayed in his home in Miami Beach, among much other lavish spending. Paul was convicted on 97 counts of racketeering and fraud in connection with CenTrust’s failure and was sentenced to 11 years in federal prison, along with nearly 1,100 savings & loan officials who went to jail.

“The government made a decision to marshal those resources,” said Keith Fleischman, who served on a special Justice Department task force in Dallas prosecuting S&L fraud and now is a solo practitioner in New York.

“I had FBI agents exclusively assigned to me and my S&L. I had two other Justice Department lawyers with me.” Result: 20- and 30-year sentences of two top executives of a Dallas S&L.

“Financial fraud crimes are not apparent,” he explained. “They take a lot of digging, a lot of energy.”

Gun shy

Clearly we’re not seeing that same effort now.

Why not? Cardona, in the Wall Street Journal article, and a couple of the former prosecutors I interviewed said the acquittal in the government’s case against two Bear Stearns hedge fund officials may have made the government gun shy. An effort that began with real purpose back in 2009 now doesn’t seem to be going anywhere. At this point, we should already have seen a couple of indictments, no?

“Prosecuting financial fraud is absolutely a priority for this administration and this department,” a DOJ spokeswoman told me.

President Obama authorized the Financial Fraud Enforcement Task Force in November 2009 with a mandate to “investigate and prosecute financial crimes and other violations relating to the current financial crisis and economic recovery efforts,” according to a DOJ publication. Its executive director, Robb Adkins, called it “the largest coalition ever brought to bear in confronting fraud.” He has left that post to go into private practice.

And yet, when I reviewed the news releases on its website, www.stopfraud.gov, I saw quite a few convictions involving mortgage fraud, other relatively minor frauds, and even some major financial scams and Ponzi schemes. And, of course, there were big insider-trading convictions against billionaire hedge fund manager Raj Rajaratnam and others, which U.S. Attorney Preet Bharara and his team handled superbly.

But few of them were connected to the financial crisis per se or to the major Wall Street banks.

So, I’m left with more questions than answers. Did the administration go easy on Wall Street firms because of their alleged fragility after the crisis, as the New York Times suggested in April? Are Wall Street CEOs being spared because of their contributions to the Obama campaign in 2008 (although they haven’t given nearly as much this time)? Are they being handled with kid gloves because the president doesn’t want to seem too “anti-business” going into his re-election campaign?

I tried to find out, but the White House press office didn’t respond to several requests for comment.

Read Howard’s take on which recent presidents did the best job fighting fraud, and cast your vote at The Independent Agenda.

Prosecutors usually are insulated from raw politics, and I have no reason to think that’s different now. So, my best guess is that the heavy burden of proof in criminal cases and excess caution is driving decision-making here.

That’s why I think, as with the SEC, that the Justice Department needs to be more aggressive, take some risks and make some cases. A little more fire in the belly would go a long way.

Howard R. Gold is a columnist for MarketWatch and editor at large for MoneyShow.com. Follow him on Twitter @howardrgold, read more commentary at www.howardrgold.com, and check out his political blog at www.independentagenda.com.