Luigi Mangione, the man suspected of fatally gunning down UnitedHealth Group chief executive Brian Thompson on a Manhattan street, is due to be arraigned on Monday on state murder charges that brand him a terrorist.

The 26-year-old suspect accused of gunning down UnitedHealthcare CEO Brian Thompson on a street in midtown Manhattan, Luigi Mangione, pleaded not guilty during an arraignment at the New York State Supreme Court on Monday.

The suspect in the killing of UnitedHealthcare’s CEO is returning to New York to face murder charges after agreeing to be extradited Thursday during a court appearance in Pennsylvania where he was arrested last week after five days on the run.

Brian Thompson's accused assassin Luigi Mangione was led on a public perp walk when he landed in Manhattan, a move that legal experts noted was unusual.

A triptych of criminal charges paints a searing, sometimes disparate portrait of the man accused of ambushing and killing UnitedHealthcare’s CEO Brian Thompson

Luigi Mangione appeared in a New York court and pleaded not guilty to start murder and terrorism charges. Watch team coverage from CBS News New York's Alice Gainer and Lisa Rozner.

The legal defense fund for Luigi Mangione, the 26-year-old accused of murdering UnitedHealthcare CEO Brian Thompson, has amassed over $200,000 in donations. The outpouring of support has raised alarms among law enforcement officials who fear the suspect is being idolized.