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.

UnitedHealth Group Inc. won a major finding in a long-running lawsuit in which the US Department of Justice claimed the company overbilled Medicare by at least $2.1 billion.

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

UnitedHealth Group notched a major court win in a legal challenge over its Medicare Advantage billing practices that is stretching into its second decade. | UnitedHealth Group notched a major court win in a legal challenge over its Medicare Advantage billing practices that is stretching into its second decade.

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

U.S. Senator Chuck Grassley requested detailed information on UnitedHealth's Medicare billing practices in a letter to CEO Andrew Witty, amid reports suggesting the insurer may have leveraged billing rules to its advantage.