WASHINGTON — An accounting gimmick called Repo 105 provided financial relief for Lehman Brothers in the months before its spectacular collapse, an autopsy of the once-venerable Wall Street house has found. The question now is whether the trickery spells legal jeopardy for executives of Lehman or its auditors Ernst & Young.

The implosion of Lehman Brothers Holdings Inc. into the biggest bankruptcy in U.S. history in September 2008 precipitated the financial meltdown that plunged the economy into the most severe recession since the 1930s.

How did it happen?

After saddling itself with tens of billions of troubled assets that couldn't easily be sold, Lehman masked its debt and perilous financial condition by using the accounting artifice, an examiner appointed by the bankruptcy court found in a 2,200-page report on a yearlong investigation.

The examiner, Anton Valukas, discovered that Lehman put together complex transactions that allowed the firm to sell "toxic" securities, mostly mortgages, at the end of a quarter — wiping them off its balance sheet when regulators and shareholders were examining it — and then to quickly buy them back. Thus, the "repo," for repurchase.

"It's a very damaging report and certainly is something that is going to be carefully scrutinized by federal prosecutors," said Robert Mintz, a former Justice Department prosecutor who is a private defense attorney.

Now, thanks to the work by Valukas, Repo 105 has entered the pantheon of phrases for accounting chicanery, along with Enron's Jedi, Chewco and Raptor partnerships and the Buco Nero (black hole) offshore account stashed away by the fallen Italian dairy giant Parmalat.

In the sagas of those two companies, the role of the accounting firms was central.

Even members of Leh-man's accounting staff, in e-mails unearthed by the examiner, called the Repo 105 concoctions an "accounting gimmick" and "a lazy way of managing the balance sheet as opposed to legitimately meeting ... targets at quarter end."

In the meltdown's wake, the Justice Department and the SEC launched wide-ranging investigations of companies across the financial services industry — investigations believed to include insurer American International Group Inc. and mortgage giants Fannie Mae and Freddie Mac as well as Lehman.

A year and a half after the financial crisis struck, charges haven't yet come in most of the probes.

It's daunting to make a case in a complicated white-collar investigation. "These are often incredibly complicated cases," Mintz said. "Prosecutors need strong and unequivocal evidence of wrongdoing."

But in the Lehman affair, there's a new road map.

The Justice Department and the SEC "have the benefit of a very substantive and comprehensive investigation," said Peter Haveles, head of the financial services litigation department at law firm Kaye Scholer in New York. "It greatly facilitates the efforts of each of those agencies to evaluate and determine whether to bring charges."

Valukas' report doesn't reach a conclusion on whether executives violated securities laws. It does say their decision not to disclose the effects of its business judgments "does give rise to colorable claims against the senior officers who oversaw and certified misleading financial statements."

Colorable claims means there appears to be sufficient grounds to win civil damages in court.