The wave of cases has ignited a legal controversy, raising the question of whether federal prosecutors, in dusting off an old statute, are misapplying the law. So far, judges have blessed the government's tactics.
"It's been an extremely effective tool," said Mr. Weidman, who lives in West Los Angeles with his wife, an artist, and their 95-pound Labradoodle.
While Mr. Weidman, who is known as Lee, sought to play down his role, numerous senior Justice Department officials singled him out.
"I can't emphasize enough how significant Lee was to these lawsuits," said Thomas J. Perrelli, a partner at Jenner & Block who was the associate attorney general overseeing many of these cases. "He was the one person who developed the theory that laid the foundation for the financial crisis cases."
More from The New York Times:
Fed Extends Stimulus as Growth Stumbles
Looking for a Way Around Keystone XL, Canadian Oil Hits the Rails
NoU.S. Action, So States Move on Privacy Law
Mr. Weidman's work came into focus in 2009 with the economy reeling and the Obama administration under fire for not holding Wall Street banks accountable. As the Justice Department searched for new prosecutorial methods, Mr. Weidman became an overnight sensation within the agency.
Federal prosecutors flew out to California to pick his brain. He held training sessions across the country. The Justice Department assigned him to one of its most promising investigations, a civil action against the credit-rating agency Standard & Poor's.
That case hinged on Firrea. Enacted in the late 1980s after risky lending practices imperiled the savings and loan industry, the law created a powerful tool to punish fraud committed by banks and their executives.
(Read more: Are markets at risk of 1999-style Fed bubble?)
Firrea is unusually crafted, as it requires a criminal violation like wire fraud or mail fraud to set off the law's penalties. But because it is a civil statute, it requires a lower burden of proof than criminal charges — finding guilt by a preponderance of the evidence versus beyond a reasonable doubt.
That broad authority has alarmed some defense lawyers, who have argued that the Justice Department has stretched the application of Firrea far beyond its original intent. Bank of America, in a motion to dismiss its case, described the prosecution as having "a wildly expansive reading" of the law.
Other critics question whether the government is overcompensating for the lack of criminal cases against Wall Street. Firrea's civil actions are a cop-out, the critics say, since not one senior Wall Street executive has been charged criminally for a role in the crisis. The same office that employs Mr. Weidman — the United States attorney's office in Los Angeles — has come under fire for dropping a criminal investigation of Angelo Mozilo, the former chief executive of Countrywide Financial, one of the biggest mortgage lenders before the financial crisis.
Some investigators at the Securities and Exchange Commission, which file civil cases against big banks, have also raised objections. Federal prosecutors, the S.E.C. officials privately grouse, are encroaching on their turf.
"Realistically, for the Justice Department, the civil cases are a Plan B," said Stavros Gadinis, a professor at the University of California, Berkley, law school who focuses on financial regulation.
The federal government's deployment of the little-used law has inspired comparisons to Eliot Spitzer's novel use of the Martin Act as a cudgel against fraud. As New York's attorney general, Mr. Spitzer harnessed the powerful 1921 state law to pursue suspected wrongdoing at large Wall Street firms like Merrill Lynch.
Firrea carries similar potency. In addition to the lower burden of proof, it allows prosecutors to bring cases that take aim at misconduct as far back as 10 years — a generous statute of limitations compared with five years for criminal securities fraud. And in pursuing a Firrea lawsuit, prosecutors are allowed not only to issue subpoenas, but also to take the sworn testimony of individuals.
It also provides for hefty fines. The Justice Department used the law to sue S.& P. for more than $5 billion, accusing it of knowingly issuing misleading ratings on mortgage-backed securities. JPMorgan's tentative $13 billion settlement over its sale of shoddy mortgage securities would be a record — a single company has never before paid that much to the government.
Defense lawyers say that Firrea gives the government a game-changing weapon in pursuing civil cases against banks.
"In retrospect, it's surprising that prosecutors have waited so long to happen upon such a powerful statute," said Susan E. Brune, a former federal prosecutor and now a partner at Brune & Richard.