There are 50 State Jurisdictions and a Federal Jurisdiction.
Luigi Mangione was charged under New York State laws, he was held by a state jail/prison.
These new charges are Federal. The feds took their time because he's already in a State jail/prison, so no need to rush the charges. They can take the time to plan on making an example out of him.
Oh you're gonna wanna learn about the speed of court procedures.
It can take years for trials to happen.
And one jurisdictions proceedings doesn't affect the other.
Think of New York state and the US Federal government as two Sovereign nations. That's what the Sovereignty in "Dual Sovereignty" mean.
Theoretically, the Federal government could've waited for the State proceedings to finish, then file charges and arrest him again after he gets acquitted by the state courts. It wouldn't, legally speaking, violate any "speedy trial" clause (even though ethically it would). And it also doesn't violate Double Jeopardy clause, since they are considered separate "Sovereigns".
He was charged with murder in New York State. These are charges from the Department of Justice in a federal court, not the state court. This is how the Republicans are trying to make an example of him
Didn't Trump's administration ask for the death penalty? Sounds political to me. At the end of the day they don't want people thinking they can just go around murdering billionaires, those billionaires might have to pretend to be human.
Isn’t this double jeopardy then? Being charged twice separately for the same crime?
No. Legally speaking, double jeopardy isn't a provision against being charged multiple times for the same crime, it's a provision against being charged multiple times for the same crime by the same sovereign entity.
The federal government and the state government of New York are two different sovereign entities, so they can both prosecute him for the same or extremely similar charges for the same crime, and double jeopardy is not invoked.