Luigi Mangione pleads not guilty to murdering healthcare CEO as fans cheer 26-year-old outside court

He also faces federal stalking and murder charges that could land him the death penalty.

He has yet to enter a plea deal on those charges.

Luigi Mangione has pleaded not guilty to state murder and terror charges

Reuters

Prosecutors have said both the federal and state cases will move forward at the same time.

Prosecutors say Mangione shot Thompson in Manhattan before going on the run until being arrested at a McDonald’s in Pennsylvania.

During the arraignment, prosecutor Joel Sideman said that Manhattan district attorney’s office has "primary jurisdiction" over the case and will try it before the federal prosecution against Mangione.

The accused will probably be returned to federal custody.

During the short hearing, Mangione sat next to his lawyer Karen Agnifilo wearing a maroon jumper and a pair of chino trousers.

He said “not guilty” in the microphone to the charges against him.

The defendant’s family did not appear to be in the courtroom but predominatly female supporters waited outside the courtroom to cheer him on.

Speaking to ABC News, a Mangione supporter said: "This is a grave injustice, and that's why people are here."

Supporters wearing masks waited outside the courtroom

Reuters

Last week, Mangione's star defence attorney Karen Friedman Agnifilo said her client may not receive a fair trial due to the high publicity that is being perpetuated by law enforcement.

She has called public parades of Mangione “absolutely unnecessary” and “perfectly choreographed, utterly political".

"He is being treated like a human ping-pong ball between warring jurisdictions here," Agnifilo added.

At the same time, people on social media have been praising the 26-year-old’s alleged crimes out of anger at the US healthcare system.

Judge Gregory Carro said he could not control what went on outside court but promised Mangione would receive a fair trial.