The department began pulling back from a more aggressive pursuit of white-collar crime around 2005, say defense lawyers and former prosecutors, after the Supreme Court overturned a conviction it won against the accounting firm Arthur Andersen. That ended an era of brass-knuckle prosecutions related to fraud at companies like Enron.

Another example of this more cautious prosecutorial strategy: Government lawyers now go to companies earlier in an inquiry, and often tell companies to figure out whether improper activities occurred. Then those companies hire law firms to investigate and report back to the government. The practice was criticized last year when the Justice Department struck a settlement with Beazer Homes USA, a home builder accused of mortgage fraud.

This “outsourcing” of investigations — as some lawyers call it — has led to increased coziness between the government and companies, some critics say.

In banking, the collaboration is even stronger, dating to the mid-1990s when banks were asked to regularly report suspicious activities to the Treasury Department, an effort that aimed at relieving regulators of some of their enforcement loads. But it gave regulators a false assurance that banks would spot and report all wrongdoing, former investigators say. Moreover, companies are not as likely to come forward with evidence related to senior executives or to widespread patterns of misbehavior, some academics say.

Intended to make the most of the government’s limited investigative resources, the government’s cooperation with corporations and industry groups can work well and save money when business hums along as usual. But some veterans of government prosecutions question such collaboration in financial crisis cases, and contend they should have been pursued more aggressively.

“Traditionally, a bank would tell the Department of Justice when an employee engaged in crimes, but what do you do when the bank itself is run by a criminal enterprise?” said Solomon L. Wisenberg, former chief of the financial institutions fraud unit for the United States attorney in the Western District of Texas in the early 1990s. “You have to be able to investigate without just waiting for the bank to give you the referral. The people running the institutions are not going to come to the D.O.J. and tell them about themselves.”