Luigi Mangione Pleads Not Guilty to First-Degree Murder of UnitedHealthcare CEO Brian Thompson

Luigi Mangione has officially pleaded not guilty after being charged with the murder of UnitedHealthcare CEO Brian Thompson.

The 26-year-old entered not guilty pleas on Monday morning, December 23, in New York State court for 11 state counts — including first-degree murder, second-degree murder as crime of terrorism and various weapons charges.

In photos obtained by OK!, Mangione could be seen dressing his best, as he was escorted into a courtroom for the hearing in a maroon sweater layered over a button-up shirt and gray slacks.

The University of Pennsylvania alum appeared to still be wearing his orange prison shoes and was chained around his waist and wrists.

At one point, Mangione — who was accompanied by his lawyers Karen Friedman Agnifilo and Marc Agnifilo — even flashed a wide smile while filling out some sort of paperwork with the help of a hovering cop.

If convicted, the infamous suspect could face life in prison without parole. There is even possibility of the death penalty if he is found guilty of the federal charges made against him on Thursday, December 19.

"Today, the Justice Department has brought federal murder charges against Luigi Mangione," Attorney General Merrick B. Garland confirmed in a statement on Thursday. "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."

Assistant Director James E. Dennehy of the FBI New York Field Office added in the press release: "Luigi Mangione allegedly conducted the carefully premeditated and targeted execution of Brian Thompson to incite national debates. This alleged plot demonstrates a cavalier attitude towards humanity — deeming murder an appropriate recourse to satiate personal grievances. Through continued close partnership with the NYPD, the FBI maintains our steadfast commitment to fervently pursue any individual who promotes a personal agenda through violence."

Mangione is currently being held without bail at the Metropolitan Detention Center in Brooklyn, N.Y., where disgraced rapper Sean Diddy Combs has been locked up at since September on racketeering, s-- trafficking and transportation to engage in prostitution charges.

The accused murderer's case has caught national attention — and even global — with Mangione gaining a fanbase of supporters rallying behind him in support of the vicious act he allegedly carried out on Wednesday, December 4, as an apparent rally cry against the healthcare industry.