Luigi Mangione Pleads Not Guilty to Federal Murder Charge at NYC Hearing

Luigi Mangione has just pled not guilty to four federal charges -- including a count of murder through the use of a firearm.

The alleged UnitedHealthcare CEO killer appeared in a New York City federal court Friday for his arraignment, where he pled not guilty to one count of murder through the use of a firearm, two counts of stalking, and one firearms offense for allegedly using a silencer.

The judge ordered all discovery to be turned over to the defense within 30 days ... making the deadline for that May 27.

As you know ... federal prosecutors want to go after Mangione with the death penalty, while Mangione's team has opposed it. They made their respective filings early this month.

As we previously reported ... Mangione was arrested in December, days after he allegedly shot and killed UnitedHealthcare CEO Brian Thompson early in the morning on a New York City street.

The slaying started a multi-day manhunt ... which ended when an employee at a Pennsylvania McDonald's called the police on him.

Luigi is facing both state and federal murder charges for allegedly killing Thompson ... and, he pled not guilty to state murder charges back in December.

Mangione's alleged diary shows months of planning leading up to the murder ... with one entry reading that "insurance is the target" because it "checks all the boxes."

While some -- like President Donald Trump -- have slammed Mangione and his supporters, others, like journalist Taylor Lorenz, who's faced controversy for her take on the case, are more on the fence about the alleged killer.