Luigi Mangione has pleaded not guilty to multiple counts of murder following the 4 December killing of Brian Thompson, 50, outside a midtown Manhattan hotel.
In addition to the New York cases, Mr Mangione also faces charges of forgery, carrying firearms without a licence, and other counts in Pennsylvania, where authorities arrested him at a McDonald's.
Dozens of supporters were outside court as the man accused of fatally shooting the chief executive of UnitedHealthcare made his first appearance.
Dozens of people who showed up in court to support the suspect including former army intelligence analyst Chelsea Manning who was jailed for stealing classified diplomatic cables.
Pic: Steven Hirsch/New York Post via AP] The 26-year-old is accused of ambushing and shooting the executive as he walked to an investor conference.
