Baltimore ? A former currency trader accused of hiding $691 million in losses pleaded guilty Thursday in one of the biggest bank fraud cases in U.S. history and will get 7 1/2 years in prison.

Prosecutors said John Rusnak fabricated trades to cover the losses and make it appear as if Allfirst bank was making money. That, in turn, enabled him to collect big bonuses.

“It’s a bitter pill,” defense attorney David Irwin said. “It’s a lot of time.”

Rusnak will be sentenced in January, receiving a prison term worked out in a plea bargain. As part of the deal, the 37-year-old father of two also agreed to cooperate with investigators in the continuing probe.

“Mr. Rusnak undertook a sustained and concentrated effort to avoid the bank’s accountability system, and whether he had help in that at this time has not been determined,” U.S. Atty. Thomas DiBiagio said.

Rusnak was indicted in June in the biggest bank fraud case since Nick Leeson lost more than $1 billion on futures trades and caused the 1995 collapse of England’s distinguished Barings Bank.

Rusnak ran up the losses at Allfirst Financial in a five-year period, mostly from trading Japanese yen. While trying to recoup those losses, prosecutors say, he dug himself a deeper hole by taking ever-larger risks.

Prosecutors said Rusnak did not directly profit from the trading losses, but by manipulating Allfirst’s computerized system of tracking trades, he was able to make it look as if the bank was making money instead of losing it between 1997 and 2001.

That earned Rusnak bonuses of more than $650,000. He collected about $433,000 of that before the fraud was discovered last winter. Whether Rusnak will pay anything to Allfirst will be determined at a court hearing in January.

Rusnak could have gotten up to 30 years in prison and a $1 million fine. Still, the federal prosecutor said the 7 1/2-year sentence, plus five years’ probation after release, was stiff for white-collar crime.

Leeson served 3 1/2 years in the Barings case. That scandal prompted banks worldwide to tighten internal checks, and Leeson expressed surprise earlier this year that the problems at Allfirst were not discovered sooner.