UnitedHealth Group stock fell Thursday following a report that the Justice Department is investigating the company for possible criminal Medicare fraud. The news comes only days after the struggling health insurer announced the departure of its CEO Andrew Witty due to personal reasons and suspended its full-year guidance,

The Justice Department is investigating UnitedHealth Group for possible criminal Medicare fraud, people familiar with the matter said. The healthcare-fraud unit of the Justice Department’s criminal division is overseeing the investigation,

UnitedHealth Group (UNH) shares cratered more than 13% Thursday morning after The Wall Street Journal reported that the Department of Justice is conducting a criminal investigation into the company’s Medicare billing practices.