While Luigi Mangione today stands trial for the killing of UnitedHealthcare CEO Brian Thompson, the U.S. Justice Department is launching a civil fraud investigation into the conglomerate’s Medicare billing practices.

The investigation is evaluating Medicare billing protocols, according to the report.UnitedHealth shares sank after The Wall Street Journal reported that the insurer's Medicare billing protocols are under Justice Department investigation.

The Justice Department is probing diagnoses and practices that triggered extra payments to UnitedHealth’s Medicare Advantage plans, people familiar with the matter say.