Federal prosecutors are adding employees to investigate possible fraud at New York-area financial firms linked to the global credit crisis.

The extra personnel will use strategies that proved successful in prosecuting executives of Enron Corp. and Refco Inc., three U.S. attorneys said in interviews Thursday — Michael Garcia of the Southern District of New York, Benton Campbell of the Eastern District of New York, and Christopher Christie of the District of New Jersey.

A central question will be whether executives lied to investors about securities linked to overvalued subprime mortgages that sparked the credit crisis, the U.S. attorneys said.

"It usually boils down to some type of fraud, some type of misrepresentation," said Mr. Garcia, whose Manhattan district is home to many U.S. financial companies, as well as the exchanges where their shares are traded.

Nationally, a senior law enforcement official said last month that the Federal Bureau of Investigation is looking into 26 firms, including Lehman Brothers and American International Group Inc.

Mr. Garcia's white-collar crime unit has added three prosecutors, raising its total to 20, and he has assigned eight lawyers to a new mortgage fraud division. One case this month led to a 10-year sentence for a man who duped homeowners facing foreclosure out of $2.5 million.

In addition to assigning 12 prosecutors to securities fraud cases, Mr. Campbell has created a task force to probe the subprime fallout. He said he has made white-collar crime a priority.

"There are various iterations: valuations questions, insider trading, material misrepresentations," Mr. Campbell said.

"What we are generally seeing is the same kind of fraudulent activity, but it's the factual background to the fraudulent activity that's different."

Mr. Christie has added a prosecutor to his 10-person securities fraud unit.

In the last wave of white-collar prosecutions, capped by the imprisonment of WorldCom Inc. chief executive Bernie Ebbers and Enron CEO Jeffrey Skilling, prosecutors convinced juries that executives knew their companies' books were cooked.

Aware that jurors may get confused by financial instruments such as credit default swaps, the government is looking to simplify prosecutions in the same way.

In Manhattan, prosecutors have won convictions this year against top executives at Refco, which engaged in complicated futures transactions. They focused on lies that Phillip Bennett, the now-defunct firm's CEO, and Tone Grant, its president told investors about its operations.

"Refco is an example of a model" for future prosecutions, Mr. Garcia said.

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