The CEO of UnitedHealth Group defended the company's role in the U.S. health care system days after a report said the company made huge profits by significantly marking up the cost of lifesaving drugs.

After reporting weaker than expected results for the company’s insurance division, UnitedHealth CEO’s said his company was not to blame for the high cost of healthcare in the U.S.

UnitedHealth Group shares have lost more than $63 billion in value since the murder of UnitedHealth CEO Brian Thompson in early December.

In his first public comments since one of his executives was shot to death, UnitedHealth Group CEO Andrew Witty said the healthcare system “needs to function better.”

UnitedHealth reported fourth-quarter results on Thursday that reflected persistent challenges for the health insurance sector.

In its first results since its insurance unit CEO was fatally shot in New York City, UnitedHealth Group reported Thursday weaker-than-expected fourth-quarter revenue, prompting its shares to fall in early morning trading despite quarterly profit beating projections.