Jurors at Luigi Mangione’s murder trial will get to see the 3D-printed pistol and alleged “manifesto” found inside his backpack, a judge ruled Monday — handing prosecutors a key legal win.

Altoona, Pa. cops followed appropriate legal protocol when searching the accused assassin’s bag at the police station after nabbing him for the December 2024 execution of UnitedHealthcare CEO Brian Thompson, Manhattan Supreme Court Judge Gregory Carro found.

Carro’s decision means the Manhattan District Attorney’s Office will reveal at trial the alleged murder weapon — a 9-millimeter handgun equipped with a silencer.

The weapon was discovered inside the 28-year-old Mangione’s bag after his arrest at an Altoona McDonald’s, which followed a dramatic five-day manhunt.

Prosecutors will also be able to show Mangione’s journal, in which the University of Pennsylvania grad mused about killingthe “greedy” CEO to denounce an industry that “extracts human life force for money.”

But Carro separately blocked other evidence — including a loaded magazine, Mangione’s wallet and passport and a computer chip hidden inside a cardboard sleeve — that police obtained from Mangione’s bag before getting a warrant.

Police breached Mangione’s rights by searching the knapsack without a warrant even though it was outside of the accused killer’s reach — where officers did not need to search it to protect themselves or the public, the judge found.

“I find that the search of the backpack at the McDonald’s was an improper warrantless search,” the judge said from the bench as Mangione sat at the defense table, handcuffed and wearing a blue suit, during a brief hearing in Manhattan Supreme Court.

The fruits of the officers’ search of Mangione’s bag at the police station — which turned up the alleged “manifesto” and handgun — will be allowed into the trial because the search followed protocol, Carro ruled. 

The judge delivered the high-stakes ruling as around two dozen of Mangione’s fans, who view him as a twisted folk hero for highlighting the perils of the healthcare industry despite charges that he murdered a father-of-two, attended Monday’s hearing in the courthouse gallery.

Several supporters proudly displayed press badges granted to them by the New York City Mayor’s Office — and were not shy in expressing their admiration for the accused killer.

“I’m saying f–k Brian Thompson. I don’t give a flying f–k he died,” Ashley Rojas, one such city-accredited “press” member, told reporters outside the courthouse.

Mangione faces a September 8 trial on charges that carry a maximum sentence of 25 years-to-life in prison. The scion of a wealthy Maryland family is separately charged in a federal case, also in Manhattan, in connection to Thompson’s death.

He has pleaded not guilty in both cases and is being held without bail at Brooklyn’s Metropolitan Detention Center alongside other high-profile inmates like ousted Venezuelan dictator Nicholas Maduro.