Shares of UnitedHealth Group ( UNH -14.89%) are falling on Thursday. The company's stock has plummeted 15% as of 11:33 a.m. ET but lost as much as 19.2% earlier in the day. The collapse comes as the S&P 500 gained 0.1% and the Nasdaq Composite fell 0.4%.

The Wall Street Journal in a recent report citing unnamed individuals stated that the US Department of Justice was investigating UnitedHealth Group for potential Medicare fraud.

UnitedHealth Group is being investigated by the Justice Department for possible criminal Medicare fraud, The Wall Street Journal reported, citing people familiar with the matter. The healthcare-fraud unit of the Justice Department's criminal division is overseeing the investigation,

UnitedHealth Group announced that CEO Andrew Witty is stepping down due to 'personal reasons,' and former CEO Stephen Hemsley will replace him.

Stephen Hemsley hasn’t been CEO at UnitedHealth Group in nearly a decade yet he’s never really left. Hemsley, 72, has remained chairman and a major shareholder in the health care behemoth — and now is back in the CEO suite and is expected to reinstate his brand of operational and financial discipline that turbocharged the company’s growth.

It created a fandom culture around his accused shooter, Luigi Mangione, and an endless cycle of cheerleading and scolding in response. Prosecutors have prosecuted. Editorial boards have editorialized.