Bharara focused on insider trading, and his office has amassed a stunning 80-0 record of prosecutions, locking up the hedge-fund titan Raj Rajaratnam and Rajat Gupta, the former managing director of McKinsey & Company and a director at Goldman Sachs. They took down eight former employees of Steven A. Cohen’s notorious SAC Capital hedge fund. (Notably, however, they haven’t been able to bring charges against the man himself.) Time magazine put Bharara on its cover, with the bold headline: “This Man Is Busting Wall Street.” Yet Bharara didn’t touch Wall Street’s real players — top bankers. The former prosecutor was almost sheepish about the insider-trading cases when I spoke to him: “They made our careers, but they don’t change the world.” In fact, several former prosecutors in the office told me that going after bankers was never a real priority. “The government failed,” another former prosecutor said. “We didn’t do what we needed to do.”

As a result, Bharara and his team neglected seemingly winnable cases in their own backyard, including one particularly big one. After Lehman imploded, the Justice Department’s Washington headquarters split responsibility investigating what the bank’s executives knew among three U.S. attorney’s offices: the Southern and Eastern districts of New York and the New Jersey operation. But for all of that manpower, to those closest to the Lehman probe, the government’s case was seemingly conducted by one lawyer, Bonnie Jonas, an assistant U.S. attorney for the Southern District. She would make pilgrimages to the offices of Jenner & Block, a prestigious law firm that had been assigned to investigate the Lehman bankruptcy. Jonas would pore over the 40 million-odd pages of Lehman documents the firm assembled. (The Southern District says it devoted multiple people and ample resources to the investigation.)

Nonetheless, the Justice Department never aggressively pursued what may have been the most promising angle. On Sept. 10, 2008, the chief financial officer of Lehman Brothers, Ian Lowitt, told shareholders and the public that the bank had $42 billion of available cash, or liquidity. The bank’s position, Lowitt reassured, “remains very strong.” Lehman would file for bankruptcy five days later. “What they were saying was not just wrong but materially wrong,” Robert Byman, a Jenner & Block partner, told me.

Over 14 months, Jenner & Block would put about 130 lawyers on the case to prepare a report on the collapse. At one point, recalls Stephen Ascher, a partner, one of them discovered “this wonderful chart” breaking down the liquidity figure into three categories: high, moderate and low. Of those billions, $15 billion was in the “low” category, generally because it had been pledged as collateral to other banks. One former Lehman executive told me that several other company managers understood that they could not tap much, if any, of that encumbered money. And at least two executives objected to how the bank was representing its liquidity, including its international treasurer, Carlo Pellerani, according to the Jenner & Block report. The law firm found that regulators, credit-rating agencies and Lehman’s outside lawyer had no idea that the liquidity pool wasn’t, in fact, all that liquid. When Lowitt came to talk to Jenner & Block, he explained that he had not fully understood the issues when he assured investors of its liquid assets. That may be a reasonable defense, but it does not appear that prosecutors and federal investigators made a serious attempt to test how much Lehman’s chief financial officer knew about his own books. Three Lehman executives and one regulator at the Federal Reserve, all of whom were involved in the bank’s desperate attempts to keep itself liquid, told me they were never even interviewed by any federal-government officials.

When Wall Street bankers are arrested, they often do what is known in finance as an expected-value analysis: They weigh the cost of fighting, how long it would take and the chances of the best and worst outcomes. Serageldin was a Wall Street banker with a foreign name who helped make securities that played a role in blowing up the global economy. He seemed to reach a logical conclusion: Plead guilty and take his chances with a judge’s sentence. Other bankers made the opposite choice. After ignoring the risks of the housing and credit bubbles, they took the high-risk-high-reward gamble again, hiring top lawyers and claiming that they never intended to deceive. As it turned out, they benefited from a decade of subtle changes that favored corporate executives under investigation. Serageldin took the sucker’s bet. Prosecutors simply got their man by default.

In his first months in prison, Serageldin has tried to remain upbeat. The investment-banking monk is now spending his nights in a basketball-court-size room with about 70 others. If the problem sets don’t occupy him, he is allowed five books at a time. After explaining that he had lived abroad, Serageldin became known as London. The extent of his crime, meanwhile, has been revised. Initially prosecutors implied that the trader had been part of a conspiracy to hide $540 million worth of losses. By the time he was sentenced, the government was down to accusing him of conspiring to hide about $100 million. An internal Credit Suisse analysis put the misstatement at $37 million. “There’s not a moment’s doubt on my part” that such mismarking happened elsewhere during the crisis, Fiachra O’Driscoll, a friend and former colleague of Serageldin’s, who has been an expert witness in private litigation, told me. “I have seen evidence along the way that similar things happened dozens of times.”

Federal prosecutors have their own explanation for how only one Wall Street executive landed in jail in the wake of the financial crisis. The cases were complex to investigate and would have been infernally difficult to explain to juries, some told me. Much of the crisis and banker transgressions stemmed from recklessness, not criminality. They also suggest that deferred prosecutions — with their billions in settlements and additional oversights — can be stricter punishments than indictments. Still, while the Department of Justice has not been without its successes — it won a guilty plea from BP in the Deepwater Horizon spill, and it’s currently going after traders in the wake of the JPMorgan Chase London Whale trading loss — these remain exceptions even beyond the financial sector. Federal prosecutors almost never bring criminal charges against top executives of large corporations, from banking to pharmaceuticals to technology. In March, the Justice Department entered into a deferred prosecution against Toyota but did not indict the company or any top executives. As the economy limps back from the Great Recession, compensation has recovered, corporate profits are at record levels and executives see that few, if any, of their peers ever go to prison anymore. Perhaps one reason Americans have come to begrudge the wealthy is a resentment of their culture of impunity.

Larry Thompson became known for his memo, but back in the Clinton administration, the deputy attorney general Eric Holder laid out his own memo for strengthening corporate prosecutions. But he undermined his own words by also explaining that prosecutors needed to take into account the collateral economic consequences. In testimony in front of the Senate in March, Holder, who is now the U.S. attorney general, seemed to lament the position government enforcers had found themselves in. “I am concerned that the size of some of these institutions becomes so large that it does become difficult for us to prosecute them when we are hit with indications that if we do prosecute — if we do bring a criminal charge — it will have a negative impact on the national economy, perhaps even the world economy.” Holder quickly walked back the remarks. Soon after, Lanny Breuer returned to Covington & Burling as a vice chairman.