The man accused of fatally shooting the chief executive of UnitedHealthcare has pleaded not guilty to murder and terror charges in a state case that will run parallel to his federal prosecution.

Luigi Mangione, 26, was shackled and seated in a Manhattan court when he leaned over to a microphone to enter his plea over the killing of Brian Thompson.

He was formally charged last week by the Manhattan district attorney with multiple counts of murder, including murder as an act of terrorism.

Mangione’s initial appearance in New York’s state’s trial court was pre-empted by federal prosecutors bringing their own charges over the shooting.

The federal charges could carry the possibility of the death penalty, while the maximum sentence for the state charges is life in prison without parole.

Prosecutors have said the two cases will proceed on parallel tracks, with the state charges expected to go to trial first.

Authorities say Mangione gunned down Mr Thompson as he was walking to an investor conference in mid-town Manhattan on the morning of December 4.