June 30, 2010 -- After Enron disintegrated in 2001 amidst brazen balance sheet chicanery, high-level heads rolled. Former CEO Jeff Skilling went to jail. Ken Lay, another Enron chief, was found guilty of fraud but died before sentencing.

Later in the decade, other unscrupulous executives ended up behind bars, among them former WorldCom CEO Bernie Ebbers and former Tyco CEO Dennis Kozlowski.

These convictions were part of a difficult process of restoring a shattered public confidence in the American economic system. But it has now been two years since Wall Street helped cause a financial collapse – one which sparked a grueling recession and cost taxpayers more than $1 trillion – and only one trophy scalp, that of Ponzi schemer Bernie Madoff, has been obtained by authorities. Several major financial industry targets have wriggled free without ever being charged, while some others were tried and went free.

'As Long as it Takes'

However, for Americans still craving accountability from the most mischievous masters of the universe, the Federal Bureau of Investigation has a message: Stay tuned.

That's because a special category of FBI cases connected to the epic subprime meltdown – and involving high-level Wall Street executives – remains the Bureau's highest priority, according to Peter Grupe, the assistant special agent in charge of white collar crime for the FBI's New York field office.

"We have a large number of active [subprime] cases which are being aggressively investigated," Grupe said. "These are complex, long-term, and resource intensive, but we will continue to pursue them for as long as it takes."

In an exclusive interview with ABCNews.com, Grupe underscored the FBI's commitment to Wall Street criminal probes. He pointed to unprecedented and extensive resources being deployed. He said new agents from financial and accounting backgrounds have been specifically recruited for the effort.

Thin Cases So Far

Grupe declined to say exactly how many Wall Street cases are currently being pursued. However, testifying last month before a Senate Judiciary Subcommittee on Crime and Drugs, Lanny Breuer, Assistant U.S. Attorney General, said that the FBI has 2,200 pending corporate and securities-fraud investigations across the country.

Nevertheless, there are numerous people, including some industry members eager to fully restore confidence in the financial system, who wonder, understandably, what's taking so long.

"I would have expected thousands of indictments by now," said Janet Tavakoli, president of Chicago-based Tavakoli Structured Finance. She pointed out that after the savings-and-loan crisis two decades ago there were 1,100 indictments. The biggest fish to fry were junk bond king Michael Milken and merger arbitrageur Ivan Boesky, said to be the inspiration for Michael Douglas's Gordon Gekko character in the movie "Wall Street."

"All we've seen thus far are thin cases that seem to rely on emails," Tavakoli said. "Yes these cases take a long time but it's been nearly two years."

The first two people charged after the 2008 financial crisis, Ralph Cioffi and Matthew Tannin of Bear Stearns, were ultimately found not guilty, despite the uncovering of a series of incriminating e-mails that seemed to suggest they were knowingly peddling hedge funds that were doomed.

A case involving mortgage derivatives and the biggest fish on the Street, Goldman Sachs, so far has only merited a civil charge filed by the Securities and Exchange Commission. A criminal investigation is said to be ongoing, according to several media reports.

One of the biggest single episodes of financial chaos, the implosion of AIG, produced a memorable villain, Joseph Cassano, who headed up the unit that engaged in the risky derivatives activities that led to the insurer's downfall. But Cassano's lawyers were recently notified that the Justice Department had closed its file on him.

Grupe said he could not talk about specific cases.

Landmark Wiretap Use

However, the Feds have not exactly been idling while a nation simmers. The U.S. Department of Justice announced the formation of a Financial Fraud Task Force last November. Not long after that, it revealed a sweeping insider trading case involving a major hedge fund, Galleon Group. The case is still ongoing and could ultimately produce the kind of message-sending convictions Wall Street usually gets after a period of excess (and then forgets).

The Galleon case has been described by the Justice Department as the biggest hedge fund insider trading case in history, and the first insider trading probe to involve extensive use of wiretaps. Accused mastermind Raj Rajaratnam has pleaded not guilty. Of the 22 defendants charged in connection with this case, half have already pleaded guilty.

Complex cases like the one against Galleon take time – but as the two-year anniversary of the financial crisis draws near, pundits and members of the public will demand that someone besides Madoff be held accountable.

The FBI's Grupe pointed to at least one successful, if not high-profile, conviction that he felt should have gotten more attention. The case involved a Credit Suisse bond salesman named Eric Butler who misrepresented some auction rate securities positioned as safe, backed by guaranteed student loans, but which were in reality laced with risky mortgage-backed derivatives. Butler was found guilty at trial last summer and earlier this year was sentenced to five years in prison.

More resources will continue to be used to go after Wall Street wrongdoing, Grupe said.

The Justice Department's Breuer, meanwhile, told lawmakers last month that resources are being added to address mortgage fraud and related financial crimes. In 2009, U.S. Attorney's Offices received money for 59 new prosecutors and 17 support positions for this effort. The department's budget for 2010 contains additional fraud enforcement resources, including five additional criminal division prosecutors and 35 U.S. Attorney's Office positions. And, in the projected 2011 budget, the department has asked for five fraud positions in the criminal division and 109 fraud positions in the various U.S. Attorneys' Offices.