Luigi Mangione pleaded not guilty to federal charges including murder and stalking Friday at his arraignment in the killing of UnitedHealthcare CEO Brian Thompson, crimes for which he could get the death penalty if convicted.

While public officials condemned the killing, some Americans have cheered Mangione, saying he drew attention to steep U.S. healthcare costs and the power of health insurers to refuse payment for some treatments.

Luigi Mangione has pleaded not guilty to a federal murder charge in the killing of UnitedHealthcare CEO Brian Thompson, as prosecutors formally declared their intent to seek the death penalty against him.