Luigi Mangione wore a white shirt, burgundy sweatshirt and was shackled during his appearance in a Manhattan court where he was flanked by police officers.
Monday's hearing came after Mangione, 26, appeared in a New York court last week to face federal charges also including murder following his dramatic extradition by plane and helicopter from Pennsylvania, where he was arrested at a McDonald's restaurant.
The suspect is charged in both state and federal court in the December 4 shooting of UnitedHealthcare chief executive Brian Thompson.
Thompson's murder brought to the surface deep public frustration with the expensive and opaque US medical insurance system, with many social media users painting Mangione as a hero.
People demonstrating against the industry gathered outside court Monday brandishing banners reading "free Luigi" and "innocent until proven guilty."
If convicted in the state case, Mangione could face life imprisonment with no parole. In the federal case, he could technically face the death penalty.
Mangioni's attorney Karen Friedman Agnifilo has previously sought clarity on how simultaneous federal and state charges would work, calling the situation "highly unusual."
'Political fodder'
Agnifilo raised concerns on Monday that Mangione could not receive a fair trial, and questioned why New York mayor Eric Adams had been present when Mangione was brought off a police helicopter at a Manhattan helipad last week.
Aginifilo told local media Monday that officials "are treating him like he is like some sort of political fodder."
She said the sight of Mangione flanked by rifle-wielding tactical officers during the final stage of his extradition that was widely broadcast was "utterly political."
Mangione was arrested in Altoona, Pennsylvania, on December 9 following a tip from staff at a McDonald's restaurant, after a days-long manhunt.
He had traveled to New York by bus from Atlanta about 10 days before the crime, the Department of Justice said.
After checking into a Manhattan hostel with false identification, he allegedly performed reconnaissance near the victim's hotel and the conference venue where the shooting took place.
Early on December 4, Mangione allegedly tracked Thompson, walked up behind him and fired several gunshots from a pistol with a silencer, prosecutors allege. Afterward, he fled on a bicycle.
Police say a "life-changing, life-altering" back injury may have motivated Mangione, although there was no indication he was ever a client of UnitedHealthcare.
When he was arrested, Mangione had a three-page handwritten text criticizing the US health care system, authorities have said.
Reports that the casings of the bullets fired at Thompson had "depose, deny, delay" inscribed on them prompted stories on social media about health insurers who allegedly used those terms to get out of covering medical care.
Such disputes are among the grievances that many have with a health system criticized for mysterious billing practices, profit-seeking middlemen, confusing jargon and costly drugs.
