The Justice Department’s years-long court battle to force UnitedHealth Group to return billions of dollars in alleged Medicare Advantage overpayments hit a major setback Monday when a special master ruled the government had failed to prove its case.

Sen. Chuck Grassley (R-Iowa) has given UnitedHealth Group two weeks to explain its method for documenting Medicare Advantage enrollees' diagnoses.

UnitedHealth shares turned lower in midday trading following reports of another probe into the nation's biggest health insurance group and its ties to government-funded healthcare programs. The Wall Street Journal reported that Sen.

By Brendan Pierson (Reuters) -A court-appointed special master has found that U.S. authorities do not have evidence to support their billion-dollar fraud case accusing UnitedHealth Group of keeping overpayments from the government for patients on its Medicare insurance plans.

The case began with a whistleblower who said UnitedHealth bilked billions of dollars through the Medicare Advantage program.

The Justice Department lacks evidence to support claims the company withheld Medicare Advantage funds, a legal expert overseeing the case said.