A manhunt is underway in New York after a shooter killed the CEO of UnitedHealthcare, Brian Thompson, outside a Manhattan hotel Wednesday morning in what police said was a “brazen, targeted attack.” The gunman shot Thompson as he was entering the New York Hilton Midtown for UnitedHealthcare’s annual investor conference.

The motive for Thompson’s killing has not been confirmed, but his widow told NBC News he had received threats due to “a lack of coverage.” Police say they found shell casings with the words “depose,” “deny” and “defend” inscribed on them. The words “delay, deny, defend” are known as the “3 Ds” of the health insurance industry.