Luigi Mangione pleads not guilty to murder of UnitedHealthcare CEO

The man accused of killing UnitedHealthcare CEO Brian Thompson has pleaded not guilty after being charged with murder as an act of terrorism.

Luigi Mangione, 26, entered his plea as he was arraigned in a Manhattan court after Thompson was shot dead outside a hotel in New York on December 4.

Mangione appeared handcuffed and shackled after he was arrested in Pennsylvania in the days after Thompson's death. He chose to waive extradition and was flown to New York to appear in court today (December 23); his first opportunity to formally respond to the accusations the Manhattan District Attorney’s Office has made against him.

Mangione was flown from Pennsylvania to New York after being arrested (XNY/Star Max/Getty/)

He faces multiple charges from the Manhattan District Attorney’s Office, including first- and second-degree murder, criminal possession of a weapon, and possessing a forged driver’s license, but his lawyer, Karen Friedman Agnifilo, has said they plan to 'fight these changes whether it’s in state or federal to the fullest extent'.

“He’s being treated like a human ping pong ball," she claimed.

Mangione will face two trials for the crimes he has been accused of; one state case and one federal prosecution. The two cases are set to run parallel to one another, and Manhattan District Attorney Alvin Bragg’s office has confirmed to CNN that it is coordinating with federal authorities for Mangione’s arraignment on the state charges.

On December 19, a federal criminal complaint was unsealed and shared by the US Department of Justice which accused Mangione of having 'stalked' Thompson in the days before his death.

Mangione has denied the charges against him (Spencer Platt/Getty Images)

Attorney General Merrick B. Garland said: “Today, the Justice Department has brought federal murder charges against Luigi Mangione. As alleged, Mangione planned his attack for months and stalked his victim for days before murdering him — methodically planning when, where, and how to carry out his crime. I am grateful to our state and local law enforcement partners for their tireless efforts to locate and apprehend the defendant and to ensure that he answers for his alleged crime.”

Edward Y. Kim, Acting U.S. Attorney for the Southern District of New York, claimed Thompson was 'gunned down in cold blood' and said he had allegedly been killed 'just because he held the position of chief executive officer of a health insurance company'.

In addition to the charges brought against him by the DA in Manhattan, Mangione also faces charges in Pennsylvania in connection to a 3D-printed firearm and false ID which are said to have been found in his possession when he was taken into custody by Pennsylvania police.