One of New York Attorney General Eliot Spitzer's investigators was perusing a stack of subpoenaed documents in a Manhattan office last month when he let out a yelp, slammed down his coffee and sprinted down the corridor.

The find, people in the office recall: a Marsh & McLennan Cos. employee's e-mail soliciting a fake bid from an insurance company to help Marsh steer business to a favored provider.

The sleuth: Craig Winters, a 27-year-old intern.

Breathless, he appeared in the 23rd-floor office of his boss, Matthew Gaul, to show him the evidence. "I was like, 'Oh my God,' " says Mr. Winters, a second-year New York University law student.

Weeks later, Mr. Spitzer sued Marsh, accusing the world's biggest insurance brokerage of bid-rigging. That led to the dethroning of its chief executive on Monday and set the stage for an overhaul of the industry's way of doing business.

Mr. Winters's gumshoeing illustrates the low-budget, scrappy approach Mr. Spitzer's office takes as it does battle with some of the world's biggest corporations, including securities firms and mutual-fund companies. There are plenty of critics who think that the office overreaches in its prosecutorial zeal, but that hasn't stopped it from becoming a magnet for a slew of hungry neophytes from top law schools as well as some seasoned lawyers from the Department of Justice and deep-pocketed white-shoe firms.

One thing their new workplace doesn't have: a fancy, well-stocked library. Months before the office unveiled its explosive charges against the insurance industry on Oct. 14, its top lawyers decided they needed to bone up on the complex business. So the office's insurance expert, Assistant Attorney General Melvin Goldberg, went to a branch of the Brooklyn Public Library and checked out its sole copy of Andrew Tobias's classic book on the insurance industry: "Invisible Bankers: Everything the Insurance Industry Never Wanted You to Know."

Senior lawyers in the office passed the volume around and soon started buying additional used copies online. Eventually, they boiled down the book's lessons, along with a compendium of stock research and newspaper articles, into a short handout for interns and other newcomers to the insurance probe.

The nerve center of the attorney general's crusade to clean up the financial-services industry is a Lower Manhattan high-rise. It occupies nine floors that resemble a university law-review office more than a corporate suite and houses 343 of Mr. Spitzer's 617 lawyers. They work on a relatively modest budget: About $63 million of the attorney general's annual budget of $197 million goes to policing corporate wrongdoing. By comparison, the finance industry's main regulator, the Securities and Exchange Commission, has a proposed fiscal 2005 budget of $913 million.

The office's hallways are crammed with boxes of subpoenaed documents from money-management companies, drug makers and the New York Stock Exchange, which is two blocks down the street. Resources are so tight that only attorneys working on the biggest cases are permitted to have BlackBerry e-mail devices; when the cases end, they must be returned to the common pool.

Law-school students, mostly in their mid-20s, take the first swipe at the motherlode of paper drummed up by the sweeping subpoenas that launch new cases. There's not enough room to give them their own workspaces, so they usually must scrounge to find the desks of absent employees.

The interns are instructed to sort through the evidence for anything that looks remotely fishy. Those documents are then turned over to the lawyers, who cull out "hot" documents -- the most promising pieces of evidence, like the one Mr. Winters discovered on Sept. 15.

The office picks hundreds of interns a year -- both undergraduates and law students -- from thousands of applications. NYU, which offers $4,000 stipends to law students who land public-service-oriented internships, generates more than a hundred applications on its own.

"It's definitely one of the higher-profile New York jobs to do, especially if you're interested in prosecutorial stuff and white-collar crime," says Benjamin Brodsky, a classmate of Mr. Winters.

Mr. Brodsky, 23, wanted to get into the securities industry group after reading about the mutual-fund case last year. But when he applied last winter, he initially wasn't even picked for an interview. Later, he read about an opening in the real-estate department of the office and called to inquire about other positions. They put him in touch with Elizabeth Block, a senior lawyer in the division, and talked his way into a stint there.

"She said that going through documents would be a big part of it," Mr. Brodsky says. He spent weeks at one point culling 50,000 e-mails related to a mutual-fund investigation.

The intern's enthusiasm for the chase "rubbed off on us," says Michael Berlin, a top lawyer in the office. "Every time they would find a document that they thought was hot, they would run in to us and be like, 'Look at this!' "

David Brown, the investment-protection unit's chief, has been hiring more and more interns. Mr. Brown used to be an in-house lawyer for Goldman Sachs Group Inc., where he made about $500,000 a year. Looking for what he considered more meaningful work after the Sept. 11 attacks, he quit in 2003 for a $92,000-a-year job with Mr. Spitzer. The 46-year-old lawyer has since been promoted to his current $125,000-a-year post.

Unlike his lower-profile predecessors -- known for cases involving sex and drug crimes -- Mr. Spitzer runs an office that now aims higher. When corporate lawyers tell Mr. Brown they need weeks to respond to subpoenas requesting documents, he replies, "You have them in your office. Fax them to me right now." He delivered one such message during the mutual-fund probe from the hospital nursery where his wife had just given birth.

The office's high profile has produced an ever-intensifying blizzard of tips -- thousands of e-mails, telephone calls to toll-free numbers and letters each month. Two civil servants in Albany are in charge of sorting the mail to make sure hot tips get to the right bureau chief, but sometimes letters land directly in the inboxes of senior lawyers. An anonymous letter to Mr. Brown helped kick off the insurance probe in March.

When Don Tellock, now 34, was a lawyer in the office working on privacy issues, he would surf the Internet in search of leads. On Thanksgiving weekend 2002, he was having trouble sleeping and ended up hunched over a computer at 4 a.m. That's when he came across a story on how personal information about Victoria's Secret customers was available on the lingerie company's Web site.

Back at the office, he wrote what is known as a case-opening memo and sent it "up the food chain." So began an 11-month inquiry that resulted in an overhaul of the company's privacy protection policies and a $50,000 fine. At the time, the company said it resolved the problem within days of learning about it. Mr. Tellock has since landed a job heading a privacy-law practice at the law firm of Arent Fox. "The beauty of being in Spitzer's office was that I could handle these cases solo and showcase my talent," he says.

Now back at NYU with dreams of someday joining Mr. Spitzer's office as a full-time attorney, Mr. Winters has one regret. "It's actually a little depressing that this might be the biggest case I ever work on," he says. "I'm peaking early."