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.