BILLINGS, Mont. (AP) – Defendants in a corruption case on a Montana American Indian reservation won’t have to repay most of the money they received through a fraudulent billing scheme, federal prosecutors said Friday.

Seven defendants pleaded guilty or were convicted at trial after authorities said they diverted roughly $500,000 from tribal accounts while doing cultural monitoring work for the Crow Indian Tribe.

Prosecutors pursued the case only on behalf of the tribe – not the outside companies that also paid for the monitoring work. As a result, U.S. District Judge Susan Watters said in a recent order that the defendants could be held liable only for a combined $48,370 in direct losses to the tribe.

That means the defendants, including several members of the prominent Old Horn family, will keep most of the scheme’s fraudulent proceeds, prosecutors said.

Defense attorneys declined comment Friday. They argued previously that the government’s claims about losses incurred by the Crow were based on a flawed theory that the tribe was generating income from the monitoring program, rather than simply covering its costs.

Family patriarch Dale Old Horn was director of the tribe’s preservation office from 2005 through 2011, overseeing protection of the Crow’s cultural, archaeological and historic resources. The office hires monitors to oversee projects on Crow lands, such as new pipelines or transmission lines crossing the reservation.

Authorities said Old Horn arranged for companies including NorthWestern Energy and ConocoPhillips to make direct payments to the monitors – who included members of his family – instead of sending payments to the tribe’s financial office, authorities said. Some monitors also were paid as tribal employees, prosecutors said.

Among the sites monitored was a 2,000-year-old bison kill site that the U.S. attorney’s office said was irreparably damaged after excavation work was approved by Old Horn in 2011.

Much of the money brought in through the scheme came from companies that were charged inflated rates for monitoring work, authorities said.

But defense attorneys successfully argued that only the direct losses to the tribe should be considered. They said the money the defendants got from outside companies amounted to legitimate wages for the work done.

“The direct payment by companies of field pay to the (historic preservation office) monitors caused a loss to the tribe of absolutely nothing,’’ wrote Matthew Wald, a Hardin attorney representing Dale Old Horn.

Prosecutors acknowledged in a Tuesday court filing that they missed the chance to seek more restitution in the case.

“Had the United States been more expansive in its charging it could have drafted an indictment that charged one scheme, to defraud the tribe, and a second scheme, to defraud the companies,’’ Assistant U.S. Attorney Carl Rostad wrote.

Failing to do so, he added “has resulted in (the) Old Horn family’s retention of the majority of the fraudulent proceeds.’’

It appears unlikely additional charges will be pursued. Rostad said Friday that no decision has been made.

Sentencing is scheduled for May 9 for the three remaining defendants in the case – Old Horn, his son, Allen and Shawn Talking Eagle Danforth. They were found guilty last August of conspiracy, mail fraud, theft from an organization receiving federal funds and theft from a tribal organization

Dale Old Horn’s nephew is Crow Tribe chairman Darrin Old Coyote. During a February hearing, a representative of Old Coyote’s administration offered testimony on behalf of the defendants that minimized the tribe’s damages in the scheme.

Four other defendants previously pleaded guilty to reduced charges after reaching deals with prosecutors. Three were sentenced to five years of probation and ordered to pay a combined $146,000 in restitution, primarily to the tribe. Dale Old Horn’s grandson, Martin Old Horn, was sentenced to six months in prison after pleading guilty to mail fraud and student aid fraud.

Under Judge Watters’ April 4 order, the three defendants found guilty at trial would not have to pay any restitution because the earlier judgments against the others more than covered the tribe’s losses.

The three also could benefit from shorter prison sentences. That’s because sentencing guidelines are based in part on the amount of losses involved in a crime.

Prosecutors have asked the judge to reconsider and make the seven defendants jointly liable. Watters has not yet responded to the request.