Huge win for Luigi Mangione ... the trial judge just ruled the death penalty is officially off the table.

The feds wanted the judge to rule that the stalking charges they filed against Mangione were a "crime of violence" -- and proving a crime of violence is a prerequisite for opening the door to even charging Mangione federally with murder. The judge ruled stalking is NOT a crime of violence ... the upshot is that Mangione can't even be charged with murder in the federal case. All he can be charged with is stalking, which carries a maximum sentence of life without parole.

Mangione is still charged in state court with murder, although in New York, there is no death penalty.

Prosecutors did win a victory ... the judge ruled the evidence searched and found in his backpack was admissible in the trial. The defense argued the evidence should not be admissible because the feds didn't have a search warrant. So now, the jury will see the gun found in Mangione's backpack, and his diary ... which prosecutors say is like a manifesto.